Membranes of Rhodopseudomonas spheroides. II. Precursor-product relations in anaerobically growing cells

Rhodopseudomonas spheroides, growing exponentially under anaerobic conditions in the light, was exposed to a 3-min pulse of labeled leucine or phenylalanine, followed by a chase of several hours. Subcellular fractions were isolated from cells harvested at various times during the chase, and their specific radioactivities determined. The results confirmed that chromatophores are formed from a precursor structure. From the decay of their specific activity, it was concluded that isolated small membrane fragments are precursors of chromatophores. Examination of the labeling of individual protein bands separated by gel electrophoresis showed that all the chromatophore protein bands except one acquire label at the same rate, and also confirmed that the proteins of the small membrane fragments have the behavior expected of precursors.