G. Boison et al., Evidence against a common use of the diaphorase subunits by the bidirectional hydrogenase and by the respiratory complex I in cyanobacteria, FEMS MICROB, 174(1), 1999, pp. 159-165
The diaphorase subunits Hox(E)FU of the cyanobacterial bidirectional hydrog
enase complex have been suggested to serve also as the three missing protei
ns of the cyanobacterial respiratory complex I. These subunits, encoded by
nuoEFG in Escherichia coli, contain the NAD(+) and FMN binding sites. Previ
ous physiological and molecular experiments demonstrated that neither the b
idirectional hydrogenase activity nor hoxYH, encoding the hydrogenase dimer
of the bidirectional enzyme, occur in the heterocystous cyanobacterium Nos
toc PCC 73102. The present study demonstrates, by heterologous Southern blo
t hybridizations, that the genes hoxFU, encoding diaphorase subunits of the
bidirectional enzyme, are both not present in Nostoc PCC 73102, whilst the
genes hoxFU were detectable in all other heterocystous and unicellular cya
nobacteria examined which possess the bidirectional hydrogenase. However, N
ostoc PCC 73102 respires with rates comparable to those of other cyanobacte
ria and sequences similar to the genes ndhJ, ndhD2, ndhA and ndhI, encoding
subunits of the respiratory complex I of Synechocystis PCC 6803, are prese
nt within the genome of Nostoc PCC 73102. Previous studies, using the unice
llular strains Anacystis nidulans and Synechocystis PCC 6803, demonstrated
that mutants in the diaphorase genes hoxU or hoxF are unable to evolve H-2,
whereas the respiration is not affected. Altogether, these data are strong
ly against the hypothesis of a common use of the hox(E)FU gene products by
the bidirectional hydrogenase and by the respiratory complex I in cyanobact
eria. (C) 1999 Published by Elsevier Science B.V. All rights reserved.