Fig. 2.

Pathways for BCAA catabolism and amino acid synthesis in lactating porcine mammary tissue. Enzymes that catalyze the indicated reactions are: (1) BCAT = branched-chain aminotransferase; (2) BCKAD = branched-chain alpha-keto acid dehydrogenase; (3) GS = glutamine synthetase; (4) GOT = glutamate-oxaloacetate transaminase; (5) GPT = glutamate-pyruvate transaminase; (6) AS = asparagine synthetase; (7) glucose metabolism via glycolysis and the Krebs cycle; (8) protein synthesis from glutamine, aspartate, alanine, asparagine, BCAA, and other amino acids. The corresponding a-ketoacids of leucine, isoleucine and valine are α-ketoisocaproate, α-keto-β-methylvalerate, and α-ketoisovalerate, respectively. Mammary tissue takes up BCAA and releases glutamine through specific transporters on the plasma membrane. This figure was reproduced from Li et al. [69] with permission from American Society for Nutrition