Localization of ribulose 1,5-bisphosphate carboxylase/oxygenase in the N sub(2)-fixing cyanobacterium Anabaena cylindrica

Monospecific antiserum against ribulose 1,5-bisphosphate carboxylase/oxygenase (RuBisCO) of Microcystis PCC7820 cross-reacted with cell-free extracts of the heterocystous cyanobacterium A. cylindrica . This antiserum was used in conjuction with colloidal gold to localize RuBisCO protein in filaments of A. cylindrica . Labelling occurred in the vegetative cells where it was associated particularly with carboxysomes in stationary phase cultures and with both carboxysomes and chromatoplasm in continuous cultures, with the proportion of RuBisCO in the chromatoplasm increasing with increasing growth rate. The protein was undetectable in mature heterocysts.