Sequence analysis of an operon of a NAD(P)-reducing nickel hydrogenase from the cyanobacterium Synechocystis sp. PCC 6803 gives additional evidence for direct coupling of the enzyme to NAD(P)H-dehydrogenase (complex I).

The sequence of a NAD(P)-reducing hydrogenase operon of Synechocystis sp. PCC 6803 containing genes for a small and a large hydrogenase subunit and six additional ORFs was determined. Until now only 11 of the 14 polypeptides of the NADH-dehydrogenase of E. coli were found in Synechocystis. By sequence homologies we suggest that the missing subunits of the peripheral part of the dehydrogenase, containing most of the FeS-clusters, are encoded by three ORFs of this operon. This hypothesis is discussed in relation to the NAD(P)-reducing hydrogenase of Synechocystis.