Arginine metabolism in insects. Role of arginase in proline formation during silkmoth development

1. Ornithine delta-transaminase (l-ornithine-2-oxo acid aminotransferase, EC 2.6.1.13) and Delta(1)-pyrroline-5-carboxylate reductase [l-proline-NAD(P) 5-oxidoreductase, EC 1.5.1.2] were demonstrated in fat-body and flight-muscle tissues of the silkmoth Hyalophora gloveri. Arginase (l-arginine ureohydrolase, EC 3.5.3.1) is also present in these tissues. 2. Arginase, ornithine transaminase and pyrroline-carboxylate reductase are generally considered to make up the catabolic pathway for the conversion of arginine into proline. The conversion of l-[U-(14)C]arginine into [(14)C]proline by intact fat-body tissue was used to show that the enzymes in insect fat body also function in this capacity. 3. Of the three enzymes of the catabolic pathway, only arginase increased during adult development and the increase coincided with the emergence of the winged adult moth. Since proline appears to be a major substrate utilized in insect flight metabolism, the increase in arginase activity at this stage suggests a major role for arginase in proline formation.