Further Evidence for a Functional Relationship between L-Amino Acid Oxidase Activity and Photosynthetic Oxygen Evolution in Anacystis nidulans. Effect of Chloride on the Two Reactions

Abstract

Abstract The ʟ-amino acid oxidase from Anacystis nidulans is inhibited by cations as well as anions. The inhibition by cations has been previously described (E. K. Pistorius, Eur. J. Biochem. 135, 217-222 [1983]). We have shown that the order of effectiveness was M3+ > M2+ > M+, when e.g. La3+, Ca2+ and K+ were compared. However, in the concentration range where the monovalent cations inhibited, the inhibition was not entirely due to the cation, but an influence of the anion could also be observed. When monovalent anions were compared as the corresponding sodium salts, the order of effectiveness was SCN- > NO3 - > CL-, Br- > I- > F- > HCOO- > CH3COO- . The inhibition of the ʟ-amino acid oxidase activity by the various salts was strongly influenced by the pH of the reaction mixture. It could be shown that the inhibition by cations increased in the alkaline pH region, while the inhibition by anions increased in the acidic pH region. Our previous results have also shown that a functional relationship might exist between ʟ-amino acid oxidase activity and photosynthetic O2 evolution (E. K. Pistorius and H. Voss, Eur. J. Biochem. 126, 203-209 [1982]). Since the water-splitting complex of photosystem II is affected by a number of anions, although only Cl- and Br- lead to activation of O2 evolution, we investigated whether a correlation could be obtained between the anion effect on the ʟ-amino acid oxidase and on photosynthetic O2 evolution. The results show that those anions which have a higher affinity for the enzyme than CL- or Br-, are especially effective in causing inactivation of the O2 evolution. Moreover, we show that ʟ-arginine which is a substrate of the ʟ-amino acid oxidase, and Cl- have antagonistic effects on the ʟ-amino acid oxidase reaction and on photosynthetic O2 evolution. We suggest that this flavoprotein with ʟ-amino acid oxidase activity is modified by Ca2+ and CL- in such a way that it can now interact with Mn2+ and catalyze the water-splitting reaction of photosystem II.