EVIDENCE FOR 2 FUNCTIONALLY DISTINCT HYDROGENASES IN ANACYSTIS-NIDULANS

The effect of growth conditions on aerobic and anaerobic hydrogenase activities of Anacystis nidulans was studied. It was found that the two hydrogenase activities both of which were confined to the particulate fraction of cell-free extracts correlated in an opposite way with growth temperature: The algae were always grown photoautotrophically in presence of H2 but after growth at 25° C a significant oxyhydrogen reaction contrasted with negligible photoreduction rates while the opposite was true after growth at 40°C. A similar correlation between incubation temperature and induction of the respective hydrogenase activity was also observed with resting cells. Kinetic analysis of the two different types of hydrogenase - catalysed reactions with Anacystis membranes yielded the following Michaelis-Mentenparameters: KM=55 μM H2 and vmax=0.12 μmol H2 per min and mg protein for the oxyhydrogen reaction, and KM=170 μM H2 and vmax=0.3 μmol H2 per min and mg protein for the photoreductions. Also the dependences of oxyhydrogen and of photoreduction activities on pH and on temperature were measured; both pH and temperature profiles were found to be markedly different for each type of H2-supported reaction. The results are discussed as pointing to the possible occurrence of two functionally distinct hydrogenase enzymes which can be synthesized by Anacystis in response to the conditions of induction. © 1979 Springer-Verlag.