Immunocytochemical localization of the cytochrome- c oxidase in a cyanobacterium, Synechococcus PCC7942 ( Anacystis nidulans)

Abstract

Immuno-gold labeling and electron microscopy was used to localize the cytochrome- c oxidase on thin-sectioned cyanobacterium Synechococcus PCC 7942 ( Anacystis nidulans) which had been grown photoautotrophically to the linear (light-limited) growth phase. The overwhelming fraction of the gold particles was found associated with the plasma membrane. On immunoblots, however, both plasma and thylakoid membranes, freshly isolated and separated, gave the expected cross-reaction though the latter to a significantly lesser extent that the former. Spectrophotometric and polarographic measurements of cytochrome c oxidation by extensively purified plasma and thylakoid membranes gave 95 and 3 nmol cytochrome c oxidized per min and mg membrane protein for plasma and thylakoid membranes, respectively, thus conforming to the immunocytochemical data. The results will be discussed with respect to the difficulty of obtaining cyanobacterial thylakoid membrane preparations absolutely free of plasma membranes and the quantitatively variable localization of certain bioenergetic key enzymes and electron transport components in both plasma and thylakoid membranes of cyanobacteria.