Characteristics of the nitrogenase system of the blue-green alga Anabaena cylindrica.

Abstract

The requirements for activity of blue-green algal nitrogenase have been studied. The optimal concentration ranges for ATP and Na2S2O4 are 2-3 mM and 4-10 mM respectively. A magnesium requirement has been confirmed but the enzyme is not specific for Mg2+, Co2+ and Mn2+ will also support activity but Ca2+, Cu2+ and Zn2+ will not. The partially purified enzyme is soluble and specific activities of 50–100 nmoles C2H4/mg protein/min have been obtained. The biochemical characteristics of the enzyme, as determined in studies using enzyme inhibitors, are similar to those of bacterial and legume nitrogenases in that the enzyme is a metallo-protein containing iron and reduced thiol groups and the redox capacity of the enzyme involves a possible valency change in the iron. The transfer of electrons from H2 via a bacterial hydrogenase has been shown to be mediated, at least in part, by ferredoxin. The role of ferredoxin and the interrelationships between photosynthesis, reductant pool and hydrogen metabolism are discussed in the light of recent results obtained by ourselves and other workers.