Investigations about various Possible Functions of the L -Amino Acid Oxidase in the Cyanobacterium Anacystis nidulans

The cyanobacterium A nacystis nidulans was grown on nitrate or L-arginine as sole nitrogen source and in the presence of different divalent cation concentrations (1 mᴍ MgSO4 and 0.1 mᴍ CaCl2 or 0.1 mᴍ MgSO4 and 0.05 mᴍ CaCl2). The L-amino acid oxidase previously reported to be present in Anacystis nidulans (E . K. Pistorius and A. E. Gau, Biochim. Biophys. Acta 849, 203, 1986) was shown to be involved in L-arginine catabolism in cells grown with the lower divalentcation concentration. Under these conditions L-arginine was partly degraded via 2-ketoarginine and 4-guanidinobutyrate. On the other hand, at higher cation concentrations the ʟ-amino acid oxidase activity seem ed to be not sufficient to provide enough NH4+ from ʟ-arginine for cell growth. Under those conditions photosystem II activity was initially reduced, and growth on ʟ-arginine could only start after photosystem II activity increased again and after arginase was induced. The arginase pathway was functional in A . nidulans grown on ʟ-arginine independently of the divalent cation concentration in the medium. A tentative scheme of the various functiona roles of the ʟ-amino acid oxidase protein in A . nidulans is given. This model combines the here presented and the previous results and suggests that the ʟ-amino acid oxidase is functional in photosynthetic and respiratory activities as well as in ʟ-arginine degradation in A . nidulans. All these activities of the ʟ-amino acid oxidase protein are greatly influenced by the divalent cation concentration in the growth medium.