Biochem lecture 4

The carboxylation of propionyl-CoA yields D-methylmalonyl CoA, which is then converted to the L form by a racemase, playing a crucial role in the conversion to succinyl-CoA.

Phenylalanine is converted to Tyrosine in the presence of O2, NADPH, and phenylalanine 4-monooxygenase, producing H2O and NADP+.

Amino acids are crucial as they make up proteins with specific functions and serve as energy reserves when dietary carbohydrates are low. They act as precursors for glucose through gluconeogenesis.

The nitrogen balance indicates the balance between anabolism and catabolism of proteins, reflecting the difference between nitrogen consumed in the diet and nitrogen excreted in urine, which remains relatively constant despite dynamic changes in protein synthesis and degradation.

The major fate of carbon in most amino acids is its conversion to glucose through gluconeogenesis, which is essential for energy metabolism, especially when carbohydrate intake is low.

The breakdown of amino acids primarily occurs in the liver, where half of their nitrogen is converted to NH4+ and the other half to aspartate, resulting in the production of urea and glucose.

The syntheses of urea and glucose are linked because they share a common intermediate in their metabolic pathways, facilitating the removal of nitrogen and the production of energy.

The primary sources contributing to the amino acid pool are:

1. Exogenous sources: Approximately 70 gm/day from food proteins through digestion and absorption.
2. Endogenous sources: Approximately 140 gm/day from the synthesis of nonessential amino acids.

The main metabolic fates of the amino acid pool include:

• Synthesis and degradation: Contributing to tissue proteins, enzymes, and protein hormones.
• Renal excretion: Excess amino acids (0.9 to 1.0 gm/day) are excreted by the kidneys.
• Conversion: Amino acids are converted into essential nonprotein nitrogenous tissue constituents such as purines, pyrimidines, and others.

In the liver, the following processes occur related to the amino acid pool:

1. Transamination and deamination lead to the production of α-Keto acids.
2. Ammonia produced is transformed into Urea, which is then excreted as Urine.
3. α-Keto acids undergo oxidation, leading to the production of Glucose, ketone bodies, and eventually Acetyl CoA, which enters the citric acid cycle, resulting in the production of CO2 + H2O + ATP.

Dietary proteins are broken down into amino acids, which then travel to the liver. In the liver, amino acids can be converted into glucose and urea. The presence of amino acids also stimulates the release of insulin from B cells. Insulin facilitates the uptake of glucose by muscle and brain tissues, where glucose is used to produce ATP for energy. This interplay helps regulate blood glucose levels effectively.

The metabolism of amino acids involves several key processes:

1. Amino Acids Intake: The body receives 90g of amino acids from the breakdown of body proteins (300g/day).

2. Distribution:

   • Intestinal Tract: 9g of glutamine is directed to the intestinal tract.
   • Muscle and Kidney: 6g of branched-chain amino acids (BCAA) are utilized by muscle and kidney for ATP production.
   • Liver: 75g of amino acids are processed in the liver.

3. Liver Metabolism:

   • The liver converts 75g of amino acids into 45g of glucose.
   • Additionally, 15g of urea is produced as a waste product.

Amino acids converge into terminal pathways leading to pyruvate, acetylCoA, or intermediates of the TCA cycle.

Amino acid metabolism primarily takes place in the liver of vertebrates, with significant activity also in the kidney.

The two major pathways involved in the removal of the α-amino group are transamination and oxidative deamination.

The α-amino nitrogen atoms are ultimately excreted in the urine as urea, ammonia, or uric acid, depending on the species.

Many intermediates of amino acid catabolism have important functions in the cell, such as acting as neurotransmitters and precursors of porphyrin biosynthesis.

Transamination is a major reaction involving all amino acids except lysine and threonine. It involves the reversible transfer of an amino group from a donor a-amino acid to a recipient a-keto acid, resulting in the conversion of the keto acid into an amino acid and the donor amino acid into a keto acid.

Transaminases play two major roles in amino acid metabolism:

1. Interconversion of various amino acids to increase the amount of one that may be in short supply, allowing for both synthesis and degradation of amino acids.
2. Channeling of amino groups ultimately to glutamate and aspartate, which can be converted to urea if in excess.

The common prosthetic group shared by transaminases is pyridoxal phosphate. It is significant because it is essential for the catalytic activity of these enzymes, facilitating the transfer of amino groups during transamination reactions.

The specific reactions are:

• Aspartate aminotransferase (AAT): L-aspartate + a-ketoglutarate → oxaloacetate + L-glutamate
• Alanine aminotransferase (ALT): L-alanine + a-ketoglutarate → pyruvate + L-glutamate

These reactions are clinically important for diagnosing diseases.

Transaminase facilitates the transfer of an amino group from an amino acid (like glutamate) to a keto acid (like alpha-ketoglutarate), resulting in the formation of a new amino acid (like alanine) and a new keto acid (like pyruvate). This process is crucial for the synthesis and degradation of amino acids, allowing for the interconversion of amino acids and their corresponding keto acids.

Pyridoxine contains the following main functional groups:

• Hydroxyl group (HO-)
• Methyl group (H3C-)
• Hydroxymethyl group (-CH2OH)

Pyridoxal differs from pyridoxine by having an aldehyde group (-CHO) instead of the hydroxymethyl group found in pyridoxine.

Pyridoxal phosphate acts as a coenzyme in amino acid metabolism, facilitating the formation of Schiff's bases with amino acids, which is crucial for transamination reactions.

Pyridoxamine contains an amino group (CH2NH2), while pyridoxal has an aldehyde group. This difference is significant in their roles in amino acid metabolism.

The reaction of pyridoxal phosphate with an amino acid results in the formation of a Schiff's base, characterized by a nitrogen double bond between the two molecules.

The process involves the formation of an Aldimine through the reaction of an α-amino acid with an α-keto acid, resulting in the release of water. This Aldimine can then undergo a reversible reaction to form a Ketimine. The reaction can be summarized as follows:

1. Formation of Aldimine:

   • α-amino acid + α-keto acid → Aldimine + H₂O

2. Reversible reaction to Ketimine:

   • Aldimine ⇋ Ketimine + H₂O

During the conversion of Aldimine to Ketimine, the following structural changes occur:

1. Aldimine Structure:

   • Contains a double bond between carbon and nitrogen (C=N).

2. Conversion to Ketimine:

   • The nitrogen atom in Aldimine is involved in a reversible reaction, leading to the formation of a new structure where the nitrogen is single-bonded to carbon and the carbon is double-bonded to another carbon (C=N to C-N).

Pyridoxal phosphate acts as a coenzyme in the transamination reactions involving amino acids and keto acids. It facilitates the transfer of amino groups from amino acids to keto acids, forming Aldimines and Ketimines. This process is crucial for amino acid metabolism and the synthesis of various biomolecules.

The reversible reactions between Aldimine and Ketimine are significant because they allow for the dynamic interconversion of amino acids and keto acids, which is essential for maintaining nitrogen balance and facilitating various metabolic pathways. This flexibility supports the synthesis and degradation of amino acids as needed by the body, contributing to overall metabolic homeostasis.

Glutamate dehydrogenase (GDH) catalyzes the oxidative deamination of L-glutamate, converting it into α-ketoglutarate while releasing NH₄⁺ ions. It is an allosteric enzyme that is inhibited by ATP, GTP, and NADH, and stimulated by ADP, GDP, and certain amino acids. GDH is crucial as it is the only active dehydrogenase for glutamate in most organisms.

The substrates for the oxidative deamination reaction catalyzed by GDH are L-glutamate, NAD⁺, and H₂O. The products of this reaction are α-ketoglutarate, NADH, and NH₄⁺.

The activity of GDH is influenced by several molecules: it is inhibited by ATP, GTP, and NADH, while it is stimulated by ADP, GDP, and certain amino acids. Additionally, its activity can be influenced by thyroxine and certain steroid hormones.

The net reaction combining transamination and oxidative deamination is: Alanine + NAD⁺ + H₂O ⟾ pyruvate + NADH + NH₄⁺. This shows the conversion of alanine to pyruvate and the release of NH₄⁺ through the action of GDH and aminotransferase.

L-amino acid oxidase is a flavin-linked enzyme that plays a minor role in amino acid deamination. It is present in the endoplasmic reticulum of the liver and kidneys, where it likely functions in the deamination of lysine. It contains tightly bound FMN as a prosthetic group and is also found in large amounts in snake venom.

D-amino acid oxidase functions to initiate the degradation of D-amino acids that arise from the enzymatic breakdown of cell wall peptidoglycans of intestinal bacteria. It contains FAD as its prosthetic group.

The amino groups of serine, homoserine, threonine, cysteine, and homocystine can be removed non-oxidatively by dehydratases. Pyridoxal phosphate serves as the coenzyme in this process.

Acetyl CoA is a key substrate that enters the citric acid cycle and is converted to Citrate.

Glutamate is derived from a-Ketoglutarate, linking amino acid metabolism to the citric acid cycle.

The three principal routes for the metabolic disposal of ammonia are:

1. Conversion to urea via the urea cycle.
2. Formation of glutamine from glutamate.
3. Conversion to aspartate for the synthesis of other amino acids.
   A minor route is the formation of asparagine.

Impaired urea formation can lead to ammonia intoxication, especially in patients with conditions like hepatomegaly and impaired liver function. This is due to the accumulation of toxic ammonia in the body.

The formation of glutamate is the major route for the metabolic recycling of ammonia, which involves the reversal of the glutamate dehydrogenase reaction. This allows the amino group to be available for the formation of other amino acids through transamination if needed.

Glutamate synthase catalyzes the reaction where α-ketoglutarate, glutamine, NADPH, and H+ are converted into two molecules of glutamate and NADP+. This enzyme requires FAD, FMN, and iron-sulphur centers for its activity.

The conversion of glutamate to glutamine involves the addition of ammonia (NH3) and ATP, resulting in the formation of glutamine, ADP, and inorganic phosphate (Pi).

Glutamine synthetase catalyzes the formation of glutamine, which serves as a temporary nontoxic storage and transport form of nitrogen. It plays a crucial role in detoxifying ammonia formed from amino acid catabolism, particularly in the brain.

Glutamine is formed in the liver and serves as a transport form of nitrogen. It is converted to urea in the liver and excreted as NH4+ in urine by the kidneys, thus aiding in the metabolic disposal of ammonia.

Glutamate and glutamine are two of the most abundant free amino acids in brain cells. Their formation can deplete alpha-ketoglutarate (a-kg), which may interfere with the TCA cycle and energy generation, contributing to ammonia toxicity in animals.

The urea cycle is a series of reactions that occur exclusively in the liver of mammals, serving as a major route for the metabolic disposal of ammonia.

The urea cycle reactions were first postulated by Krebs and Henseleit in 1932.

Asparagine synthetase catalyzes the conversion of aspartate to asparagine using ammonia or glutamine as substrates.

Asparagine synthetase can use either ammonia or glutamine for the conversion of aspartate to asparagine, while glutamine synthetase strongly prefers glutamine over ammonia as a substrate.

The reaction produces asparagine, AMP, PP (pyrophosphate), and glutamate (Glu).

The reaction accounts for much less ammonia assimilation compared to other pathways, indicating a lower contribution to nitrogen metabolism.

Aspartate plays a crucial role in the urea cycle by providing an incoming amino group through transamination from glutamate. It is converted to citrulline after losing the amino group, which is essential for the formation of urea.

Citrulline is synthesized in the cytosol and then transported into the mitochondrion. Within the mitochondrion, it reacts with ornithine and carbamoyl phosphate to continue the urea cycle. After the reaction, ornithine is transported back to the cytosol via a specific ornithine membrane transport system.

ATP is significant in the conversion of argininosuccinate as it is required for the reaction to proceed, releasing AMP and pyrophosphate (PP_i). This step is crucial for the synthesis of urea from arginine, highlighting the energy dependency of the urea cycle.

The main products formed from the reaction of citrulline in the mitochondrion are ornithine and carbamoyl phosphate, along with the release of 2ADP and P_i. This reaction is essential for the continuation of the urea cycle and the detoxification of ammonia.

The first nitrogen in urea comes from free ammonia, the second nitrogen comes from aspartate, and the carbon comes from carbon dioxide.

Two of the five reactions of the urea cycle occur in the mitochondria, while the remaining three reactions take place in the cytosol.

Carbamoyl phosphate synthetase catalyzes the formation of carbamoyl phosphate from free ammonia and carbon dioxide in the mitochondrial matrix, using two molecules of ATP. It requires N-acetylglutamate as a stimulatory allosteric activator and is specialized for urea synthesis.

The mitochondrial carbamoyl phosphate synthetase uses free ammonia as the nitrogen donor, while the cytosolic form uses glutamine. The cytosolic enzyme is inhibited by UTP and is involved in pyrimidine nucleotide biosynthesis.

The substrates are glutamine, HCO3-, 2 ATP, and H2O, and the products are carbamoyl phosphate, 2 ADP, Pi, and glutamate.

N-acetylglutamate acts as a stimulatory allosteric activator for carbamoyl phosphate synthetase, enhancing the enzyme's activity in the formation of carbamoyl phosphate, which is crucial for urea synthesis.

Ornithine transcarbamoylase catalyzes the reaction where carbamoyl phosphate condenses with ornithine to form citrulline in the mitochondrial matrix.

Citrulline exits the mitochondria via a specific transporter known as citrulline ornithine translocase, which allows it to pass into the cytosol for further reactions in the urea cycle.

The second amino group required for urea synthesis comes from aspartate, which is derived from glutamate through the action of aspartate aminotransferase in the cytosol.

The enzyme that catalyzes the reaction between citrulline and aspartate to form argininosuccinate is argininosuccinate synthetase, which requires magnesium for its activity.

Argininosuccinate synthetase catalyzes the conversion of Citrulline and Aspartate into Argininosuccinate, requiring ATP and Magnesium. During this reaction, ATP is converted to AMP + PPi, and water is released.

Pyrophosphate is hydrolyzed by pyrophosphatase to inorganic phosphate, which helps pull the overall reaction towards the right, favoring the formation of products.

The cleavage of Argininosuccinate is catalyzed by argininosuccinase, resulting in the formation of Arginine and Fumarate. Arginine serves as the immediate precursor of urea, while fumarate is further processed in the TCA cycle.

After its formation, Fumarate is hydrated to Malate and then oxidized to Oxaloacetate (OAA) in the TCA cycle. OAA can subsequently be converted to Aspartate by transamination, allowing the cycle to repeat.

The enzyme that mediates this reaction is arginase, primarily found in the liver of mammals.

The ornithine formed can pass back into the mitochondria, allowing the urea cycle to be repeated.

Only catalytic amounts of ornithine are required because it is regenerated during the cycle, allowing it to be reused.

Less active isozymes of arginase are found in the brain and kidney, but they form little or no urea from arginine.

The overall equation of the urea cycle is:

2NH3 + CO2 + 3ATP + 3H2O → urea + 2ADP + AMP + 4Pi

N-acetylglutamate acts as a positive effector of carbamoyl phosphate synthetase, which is crucial for regulating urea formation at the committed step in the pathway. Additionally, arginine stimulates the synthesis of N-acetylglutamate.

The amount of urea excreted in the urine of a normal adult averages 25-30g/day and is directly proportional to the amount of proteins ingested. This means that higher protein intake leads to increased urea excretion.

Measurements of blood urea nitrogen (BUN) levels provide a sensitive clinical test of kidney function, indicating how well the kidneys are filtering waste from the blood.

The excretion of ammonia is much less, about 2.5-4.5% of total urinary nitrogen under ordinary conditions, but it plays an important role in maintaining acid-base balance in the body.

Glutamate plays a crucial role in the urea cycle by acting as a carrier of ammonia. It can be converted to glutamine through the action of glutamine synthetase, which incorporates ammonia (⁺NH₄) and water (H₂O). Glutamate can also be deaminated by glutamate dehydrogenase to release ammonia, which is then used in the urea cycle for detoxification.

The glucose-alanine cycle involves the conversion of pyruvate to alanine in muscle tissues, which can then be transported to the liver. In the liver, alanine is converted back to pyruvate, which can enter gluconeogenesis to produce glucose. This cycle helps in the transport of nitrogen from muscle to liver and plays a role in maintaining blood glucose levels during fasting.

The amino acids that can be catabolized to pyruvate include alanine, glycine, serine, and cysteine.

The major alternative route for glycine degradation is:

Glycine + FH4 + NAD⁺ ↔ Methylene-FH4 + CO2 + NH3 + NADH + H⁺

This reaction is reversible and is catalyzed by glycine synthase.

Cysteine degradation to pyruvate may proceed by at least three different pathways.

Phenylalanine is converted to tyrosine, which then leads to leucine. Tryptophan leads to lysine, which converts to Glutaryl-CoA. Leucine converts to Acetoacetic acid. Both Glutaryl-CoA and Acetoacetic acid lead to acetoacetyl-CoA, which further converts to Acetyl-CoA.

Phenylalanine and tyrosine are considered both ketogenic and glucogenic because part of their carbon skeletons yield acetoacetate (ketogenic) and the other part yields fumarate (glucogenic).

In phenylketonuria (PKU), the enzyme phenyltyrosine 4-monooxygenase is lacking, preventing the conversion of phenylalanine to tyrosine. This leads to the accumulation of phenylpyruvic acid in the blood, which can impair brain development and cause severe mental retardation in childhood.

Restricting dietary phenylalanine during childhood can prevent the accumulation of phenylpyruvic acid, thereby preventing the impairment of normal brain development and severe mental retardation associated with phenylketonuria (PKU).

Leucine is degraded to acetoacetyl CoA and acetoacetate, making it a ketogenic amino acid. An important intermediate in this pathway is β-hydroxy-β-methyl-glutaryl-CoA, which is a precursor in the biosynthesis of cholesterol.

Threonine can be degraded primarily by threonine dehydratase, which converts it to α-ketobutyric acid. This compound then undergoes oxidative decarboxylation to form propionyl CoA, which is a precursor of succinyl CoA.

Ornithine acts as an intermediate in the degradation pathway, facilitating the conversion of arginine to glutamate.

N-acetylglutamate is an allosteric activator of the first step of the urea cycle reactions, enhancing the activity of the enzyme involved.

The amino acids involved in the a-ketoglutarate pathway include arginine, histidine, glutamine, glutamic acid, and proline.

The final product of the conversion of glutamic acid in the a-ketoglutarate pathway is α-ketoglutarate.

Methylmalonyl CoA mutase is a coenzyme B12-dependent enzyme that converts L-methylmalonyl CoA to succinyl-CoA in the succinate pathway.

A deficiency in vitamin B12 leads to a lack of intrinsic factor for absorption, resulting in the excretion of large amounts of methylmalonic acid and propionic acid in urine, indicating disrupted metabolism of methionine, isoleucine, and valine.

Tyrosine transaminase converts Tyrosine to 4-Hydroxyphenyl-pyruvic acid in the presence of α-Ketoglutarate and Glutamate.

The conversion produces CO2 and involves the enzyme 4-hydroxy-phenylpyruvic acid dioxygenase in the presence of O2.

The final product of the fumarate pathway is Fumaric acid, which is formed from 4-Fumaryl-acetoacetic acid in the presence of fumarylacetoscotase and H2O.

Four carbon atoms enter the TCA cycle via acetoacetyl-CoA and acetyl-CoA, while four remaining carbon atoms are converted to fumarate.

Asparagine is hydrolyzed to aspartic acid and ammonia:

Asparagine + H2O → aspartic acid + NH3

Asparaginase is used as a chemotherapeutic drug in the treatment of some leukemic patients.

Aspartic acid undergoes transamination with alpha-ketoglutarate to form oxaloacetate and glutamate:

Aspartate + α-ketoglutarate → oxaloacetate + glutamate

Aspartate ammonia lyase catalyzes the direct elimination of ammonia from aspartate to yield fumarate:

Aspartate → fumarate + NH3

Histidine is decarboxylated to yield histamine and CO2. Histamine is a potent vasodilator released during allergic hypersensitivity or inflammation.

Arginine can be decarboxylated to form agmatine, which is a precursor of spermine and spermidine. These polyamines are growth factors for microorganisms and stabilize membrane structures.

Serotonin is a neurotransmitter that plays multiple regulatory roles in the nervous system, including mood regulation, sleep, and appetite control.

Serotonin is synthesized from tryptophan through a series of reactions that involve hydroxylation and decarboxylation, resulting in the conversion of hydroxylated tryptophan into serotonin.

Melatonin is produced from serotonin in the pineal gland and is important for regulating light-dark cycles in animals, as well as having antioxidant effects.

Serotonin is secreted by cells in the small intestine, where it regulates intestinal peristalsis and acts as a potent vasodilator to help regulate blood pressure.

S-Adenosylmethionine serves as a precursor that is decarboxylated to form Decarboxylated S-adenosylmethionine, which is then used in the synthesis of both Spermidine and Spermine through the action of Propylaminotransferases.

Parkinson's disease is associated with low levels of dopamine in certain regions of the brain.

Drugs used to treat schizophrenia, such as chlorpromazine, are dopamine antagonists that block dopamine binding to its receptors.

LSD mimics serotonin at receptors in the central nervous system, leading to its psychoactive effects.

Fluoxetine (Prozac) blocks the uptake of serotonin into presynaptic receptors, which is beneficial in treating depression and various psychiatric disorders.

Valine transaminase

Vertebrates cannot synthesize all common amino acids and must obtain essential amino acids from their diet. In contrast, higher plants can synthesize all amino acids required for protein synthesis and can utilize various nitrogen sources such as ammonia, nitrite, or nitrate.

Leguminous plants can utilize atmospheric nitrogen for amino acid biosynthesis due to the presence of symbiotic nitrogen-fixing bacteria in their root nodules.

The biosynthesis of nonessential amino acids in humans involves relatively short pathways, most having fewer than five steps, and can be synthesized from other precursors.

The biosynthetic pathways for essential amino acids are more complex and longer, often involving 5-15 steps, compared to the relatively short pathways for nonessential amino acids.

The biosynthetic pathways for amino acids are highly regulated, with controlling enzymes modulated by inhibitors and stimulators, allowing for fine-tuning of amino acid production.

While the pathways for essential amino acids are generally similar across most species of bacteria and higher plants, there are species differences in certain individual steps, indicating variability in amino acid biosynthesis among different organisms.

Shikimic acid is a key intermediate in the biosynthetic pathway of aromatic amino acids, leading to the synthesis of important aromatic substances such as lignin, ubiquinone, and plastoquinone.

Glyphosate specifically inhibits the enzyme 5-enoylpyruvylshikimate-3-phosphate synthase in the shikimic acid pathway, which inhibits the growth of most crops and weed plants, making it an effective broad-spectrum herbicide.

Mutants of E. coli and Aerobacter aerogenes that require phenylalanine, tyrosine, and tryptophan for growth helped deduce the pathway of the biosynthesis of aromatic amino acids.

The starting compounds are C3 and C4 organic phosphates, which are converted to Shikimate.

Chorismate branches out to form CoQ and Anthranilate in the metabolic pathway.

The two main aromatic amino acids derived from Prephenate are Phenylalanine and Tyrosine.

Tryptophan is synthesized from Anthranilate with the involvement of Glutamine (Gln) and Serine (Ser).

Tyrosine leads to the synthesis of Coniferyl alcohol, which is a precursor for Lignin and Flavor components.

The aromatic amino acids highlighted are Phenylalanine, Tyrosine, Tryptophan, and Histidine.

The starting substrates for the biosynthesis of chorismate are erythrose-4-phosphate and phosphoenolpyruvate.

EPSP synthase catalyzes the conversion of phosphoenolpyruvate and erythrose-4-phosphate into 5-enoylpyruvylshikimic acid 3-phosphate, which is a key intermediate in the pathway.

3-deoxy-D-arabino-heptulosonic acid 7-phosphate is an important intermediate that is formed during the biosynthesis of chorismate, leading to further transformations that ultimately produce chorismate.

The enzyme responsible for this conversion is shikimate dehydrogenase, which utilizes NADP+ and produces NADPH + H+ as a byproduct.

The final product of the biosynthesis pathway is chorismate.

Allosteric (feedback) inhibition regulates the first reaction in the biosynthetic sequence by its end product, allowing for fine control over the rate of biosynthesis. This mechanism enables second-by-second adjustments and can involve complex interactions when multiple end products are present, leading to concerted or cumulative inhibition.

Repression lowers the concentration of one or more enzymes in the biosynthetic pathway at the DNA or RNA level, responding more slowly to metabolic changes than feedback inhibition. This mechanism conserves amino acids and energy by preventing the synthesis of unused enzymes, often leading to a coordinated repression of the entire multienzyme system.

Isozymes are different forms of enzymes that may be inhibited or repressed by different end products of the biosynthetic pathway. This allows for more specific regulation of the pathway, as seen with aldolase in the biosynthesis of aromatic amino acids, contributing to the overall complexity of regulation in amino acid biosynthesis.

In bacteria, the biosynthetic pathways for amino acids are regulated by a combination of allosteric and repression mechanisms, which can be complex and vary by species. This dual regulation allows for precise control over amino acid production in response to metabolic needs.

Aldolase isozymes participate in the initial reaction of the pathway, facilitating the conversion of D-Erythrose 4-phosphate and Phosphoenolpyruvate into Deoxy-heptulosonic acid 7-phosphate.

Feedback inhibition occurs from the end products Phenylalanine, Tyrosine, and Tryptophan, which inhibit the initial steps of the pathway, thereby regulating the synthesis of these amino acids.

The products of the pathway include glutamine, glycine, alanine, tryptophan, histidine, carbamoyl phosphate, glucosamine 6-phosphate, CTP, and AMP.