Glucose and urea.
After transamination or deamination, α-keto acids can enter the TCA cycle. TCA intermediates can also be used to make amino acids, allowing the liver to use proteins as an energy source when glucose is not available.
The nitrogen from amino acids is converted to urea, which is excreted in urine. Urea can also be broken down to ammonia (NH4+).
The primary purpose of amino acid metabolism is to provide energy, synthesize proteins, and produce other important molecules such as neurotransmitters and hormones.
An example of deamination is the conversion of glutamate to α-keto glutarate, which releases an ammonium ion.
The liver, muscles, kidneys, and intestines play significant roles in amino acid metabolism.
The liver takes one ammonium ion (NH4+) from glutamate and a second amino group from aspartate to produce urea.
During exercise or starvation when the muscle uses blood-borne glucose.
In transamination, an amino acid donates its amino group to an α-keto acid, resulting in the formation of a new α-keto acid and a new amino acid. For example, aspartate and α-keto glutarate are converted to oxaloacetate and glutamate.
Glutamine is converted back to alpha-keto acids by losing two ammonium ions, which are then used to form urea and excreted in urine.
During deamination, the ammonium group is given out, which is then fed into the urea cycle.
Dietary glucose contributes to the carbon pool, which can be used for energy production or stored as glycogen.
Alpha-keto acids accept two ammonium ions from muscles or peripheral tissues to form glutamine, which is then transported to the liver.
During deamination, the carbon group of amino acids is usually converted to glucose or triacylglycerols. Triacylglycerols are packaged and secreted by the liver in VLDL, while glucose can be stored as glycogen or released into the blood.
The intestines are responsible for the absorption of dietary amino acids and their initial catabolism.
Dietary protein is broken down into amino acids, which enter the blood amino acid pool.
Amino acids are transported to the bloodstream by a facilitated transporter.
Muscles use amino acids for protein synthesis and energy production, especially during periods of fasting or intense exercise.
Alanine and glutamine are the major nitrogen carriers of amino acid nitrogen from peripheral tissues to the liver.
Peptidases in enterocytes break down peptides into amino acids.
The alanine travels to the liver, where its carbons are used for gluconeogenesis and its nitrogen is used for urea biosynthesis.
Ubiquitinated proteins are endocytosed into early endosomes, which mature into multivesicular bodies (MVBs) that fuse with lysosomes. Lysosomal enzymes then degrade the proteins.
Endogenous proteins are those produced within the body and they are also broken down to contribute to the blood amino acid pool.
The sodium-potassium ATPase pump is involved in exchanging Na+ for K+ in enterocytes.
The kidneys are involved in the reabsorption of amino acids and the excretion of nitrogenous wastes.
Disorders of the urea cycle can lead to hyperammonemia.
Amino acids and Na+ are transported into enterocytes by a sodium-ion dependent carrier.
The liver is involved in the deamination of amino acids, urea cycle, and the synthesis of plasma proteins.
Ammonia is toxic to the brain and must be converted to the less toxic urea.
Aminopeptidase is an exopeptidase present in the enterocytes.
The 26S proteasome recognizes the polyubiquitinated protein.
Amino acids from the blood pool are used for the synthesis of new proteins and various nitrogen-containing compounds such as purines, pyrimidines, heme, neurotransmitters, and hormones.
The half-life of proteins within the human body ranges from minutes to days.
The carbon skeletons from amino acids can be used to produce ATP (energy), CO2 (as a byproduct of energy production), glucose (through gluconeogenesis), and lipids (for energy storage or cellular structures).
The ubiquitin-proteasome system is involved in protein degradation.
Protein digestion first takes place in the stomach.
Examples include haemoglobin, muscle proteins, digestive enzymes, and proteins from cells shed off from the gastrointestinal tract.
Chymotrypsin, elastase, and carboxypeptidases are collectively known as endopeptidases.
E3 ligase attaches ubiquitin to the target protein.
Pepsin is activated from pepsinogen due to the low pH in HCl.
The first step is the activation of ubiquitin by E1, which is ATP-dependent.
Enteropeptidase activates trypsinogen, converting it into trypsin.
Ubiquitin is transferred to E2 after being activated by E1.
The protein is degraded into peptides in the proteasome, which is ATP-dependent.
