2024年11月17日 · Alanine transaminase (ALT), also known as alanine aminotransferase, is a vital enzyme primarily present in the liver, though it is also found in other parts of the body. Enzymes, acting as catalysts, facilitate various bodily processes, with ALT being one among thousands with crucial functions.

When muscles degrade amino acids for energy needs, the resulting nitrogen is transaminated to pyruvate to form alanine. This is performed by the enzyme alanine transaminase (ALT), which converts L-glutamate and pyruvate into α-ketoglutarate and L-alanine. [3]

2024年5月16日 · Alanine to Pyruvate. As described in 18.2, and shown in Figure \(\PageIndex{4}\), the PLP-dependent enzyme ALanine Amino Transferase (ALT), also known as Glutamate Pyruvate Transaminase (GPT), catalyzes this simple transamination reaction: alanine +α−ketoglutarate ↔ pyruvate + glutamate. Figure \(\PageIndex{4}\): Alanine to pyruvate

Alanine can be synthesized from pyruvate and branched chain amino acids such as valine, leucine, and isoleucine. Alanine is produced by reductive amination of pyruvate, a two-step process. In the first step, α-ketoglutarate, ammonia and NADH are converted by glutamate dehydrogenase to glutamate, NAD + and water.

Pyruvate plays an essential role in central carbon metabolism. Pyruvate is generated from several sources, including the oxidation of lactate, the transamination of alanine, or as the terminal product of glycolysis. Entry of pyruvate into the mitochondrial matrix is mediated by the MPC.

Under fasting conditions, alanine, derived from protein breakdown, can be converted to pyruvate and used to synthesize glucose via gluconeogenesis in the liver. Alternately, alanine, after conversion to pyruvate, can be fully oxidized via the TCA cycle in other tissues.

Alanine transaminase (ALT), also known as alanine aminotransferase (ALT or ALAT), formerly serum glutamate-pyruvate transaminase (GPT) or serum glutamic-pyruvic transaminase (SGPT), is a transaminase enzyme (EC 2.6.1.2) that was first characterized in the mid-1950s by Arthur Karmen and colleagues. [1]

Alanine plays a significant role during early starvation, exposure to high-fat and high-protein diets, and diabetes. Glutamine plays a dominant role in gluconeogenesis in prolonged starvation, acidosis, liver cirrhosis, and severe illnesses like sepsis and acts as a substrate for alanine synthesis in the small intestine.

Indeed, shRNA-mediated knockdown of alanine transaminase 2 (ALT2), which catalyzes the transamination of alanine and α-ketoglutarate to form pyruvate and glutamate in the mitochondrial matrix, further attenuates mitochondrial pyruvate flux in MPC2-deficient hepatocytes .

These results provide direct evidence for intracellular pyruvate-lactate-alanine cycling, in which lactate and alanine produced by the cytosolic pyruvate are transported into mitochondria and converted back to pyruvate.