The Number of Hydrogenases in Cyanobacteria

Abstract

Cyanobacteria consume H, by two different pathways: the oxyhydrogen reaction and anaerobic, light-dependent H, utilization. The two pathways are shown here to be induced differently by incubating cyanobacteria anaerobically under H,. In the unicellular A nacystis nidulans and in N,-and NHi-grown Anabaena cylindrica and Nostoc muscorum, such treatment greatly enhances the activity of the oxyhydrogen reaction in all cell types. In contrast, the light-dependent pathway, determined by the H,-dependent photoreduction of NADP+, is demonstrable with higher activity only in heterocysts.Whereas the activity of the oxyhydrogen reaction is directly correlated to the structural integrity of membranes, there is an inverse correlation between membrane integrity and H, formation catalysed by hydrogenase. These findings, together with physiological considerations, suggest that a 'reversible' soluble hydrogenase does not exist in photoautotrophic cyanobacteria. No definite conclusions about the existence of two membrane-bound uptake hydrogenases are possible at present.

Molecular Biological Analysis of a Bidirectional Hydrogenase from Cyanobacteria

“…NAD(P)H-dependent H, evolution catalyzed by the bidirectional hydrogenase can, however, be measured in assays performed in the dark (Table 2). Previous experiments showed that preparations from heterocysts perform H,-dependent reduction of NAD(P)+ catalyzed by uptake hydrogenase in a light-(photosystem 1)-dependent reaction [4].…”

Cloning and sequence analysis of the gene encoding the low potential cytochrome c of Synechocystis PCC 6803

“…The bound form of the cytochrome may be a constitutively expressed component of the photosynthetic apparatus and the soluble cytochrome may, in some species, be induced by anaerobic conditions just as hydrogenase is induced. The soluble cytochrome may function in dark, anaerobic fermentation [22] and the membranebound cytochrome may function in light driven uptake of hydrogen [23,24].…”

Hydrogenases and Hydrogen Metabolism of Cyanobacteria

“…The Ni-containing bidirectional hydrogenase, partially purified and characterized from A. variabilis ATCC 29413 (178) differs from the uptake hydrogenase in its physical and catalytic properties (178,202). In general, cyanobacterial bidirectional hydrogenases are characterized by their sensitivity to oxygen, thermotolerance, and high affinity to hydrogen (49,87,89,163,178). Methyl viologen, chemically reduced by dithionite, supports hydrogen evolution by all examined bidirectional hydrogenases and is usually used as an electron donor in the assay of the enzyme.…”