MULTIPLE OLIGOMERIC FORMS OF GLUCOSE-6-PHOSPHATE-DEHYDROGENASE IN CYANOBACTERIA AND THE ROLE OF OPCA IN THE ASSEMBLY PROCESS

Multiple molecular forms of glucosed-6-phosphate dehydrogenase (C6PDH) were detected by activity staining in non-denaturing polyacrylamide g els of cell-free extracts from a range of cyanobacteria including Anab aena sp. PCC 7120, Synechococcus sp. PCC 7942, Plectonema boryanum PCC 73110, Synechocystis sp. PCC 6803, Nostoc sp. MAC PCC 8009 and the ma rine strain Synechococcus sp. WH7803. In most of the species tested, t he profile of C6PDH activities was modulated by the growth of the cell s in the presence of exogenous 10 mM glucose. Using an antiserum raise d against a fragment of C6PDH from Anabaena sp. PCC 7120, it was shown that the different molecular forms of G6PDH all contained an antigeni cally related subunit, suggesting that the different forms arose from different quaternary structures involving the same monomer. An inserti on mutant of Synechococcus sp. PCC 7942 was constructed in which the o pcA gene, adjacent to zwf (encoding G6PDH), was disrupted. Although no reduction in the amount of G6PDH monomers (Zwf) was observed in the o pcA mutant, activity staining of native gels indicated that most of th is protein is not assembled into one of the active oligomeric forms. T he oligomerization of G6PDH in extracts of the opcA mutant was stimula ted in vitro by a factor present in crude extracts of the wild-type, s uggesting that the product of the opcA gene is involved in the oligome rization and activation of C6PDH.