IDENTIFICATION OF THE PUFQ PROTEIN IN MEMBRANES OF RHODOBACTER-CAPSULATUS

The PufQ protein has been detected in vivo for the first time by Weste rn blot (immunoblot) analyses of the chromatophore membranes of Rhodob acter capsulatus. The PufQ protein was not visible in Western blots of membranes of a mutant (Delta RC6) lacking the puf operon but appeared in membranes of the same mutant to which the pufQ gene had been added in trans. It was also detected in elevated amounts in a mutant (CB120 0) defective in two bch genes and unable, therefore, to make bacterioc hlorophyll. The extremely hydrophobic nature of the PufQ protein was a lso apparent in these studies since it was not extracted from chromato phores by 3% (wt/vol) n-octyl-beta-D-glucopyranoside, a procedure whic h solubilized the reaction center and light-harvesting complexes. Duri ng adaptation of R. capsulats Is from aerobic to semiaerobic growth co nditions (during which time the synthesis of bacteriochlorophyll was i nduced), the PufQ protein was observed to increase to the level of det ection in the developing chromatophore fraction approximately 3 h afte r the start of the adaptation. The enzyme, S-adenosyl-L-methionine:mag nesium protoporphyrin methyltransferase, also increased in amount in t he developing chromatophore fraction but,vas present in a cell membran e fraction at the start of the adaptation as well.