The gamma-guanidinobutyramide pathway of L-arginine catabolism in Leishmania donovani promastigotes.

L-Arginine stimulates the respiration of Leishmania donovani to rates comparable to those observed with D-glucose. gamma-Guanidinobutyramide, CO2, urea and succinate have been identified as products of L-arginine catabolism by the cell-free extract. The reactions involved in CO2 and urea formation require aerobic conditions. An enzymatic reaction that converts radiolabelled L-arginine to gamma-guanidinobutyramide occurs in cell-free extracts. The enzyme catalyzes a reaction in which O2 consumption and CO2 production are equimolar. The O2 uptake and CO2 production are stimulated by Mg2+, Mn2+, FMN, pyridoxal phosphate, and inhibited by hydroxylamine and NaBH4. L-Arginine decarboxyoxidase is suggested as the trivial name for this enzyme. The enzyme has maximum activity at pH 6.7, and its Km for L-arginine is 3.8 mM. L-Arginine decarboxyoxidase initiates the catabolism of L-arginine (pH less than or equal to 7) in this species, and is followed by the other enzymes of gamma-guanidinobutyramide pathway. Assay procedures have been devised to assay the multiple enzymes of this pathway.