Channeling of citrulline for renal synthesis of GAA
Although protein synthesis dominates the requirements for dietary amino acids, the need for amino acids to meet demand for synthesis of other compounds is not negligible. This is especially true of production of creatine, which requires substantial amounts of arginine and methionine. Synthesis of guanidino acetate (GAA), the precursor for creatine, constitutes the main pathway for the obligatory irreversible loss of arginine consuming an equivalent to ∼20% of the dietary intake. In turn, methylation of GAA to make creatine can represent up to 75% of all methylation reactions imposing a heavy burden on methionine and 1-carbon metabolism.