Cytochrome Synthesis and Its Regulation in Spirillum itersonii

Abstract

Spirillum itersonii contains b- and c-type cytochromes as well as a CO-binding pigment of the cytochrome o type. Synthesis of cytochromes b and c is increased by about 2- and 4-fold, respectively, when cells are transferred from high to low aeration. The increased concentration of cytochrome is not accompanied by an increase in the respiration rate of the cells. Both cytochrome b and cytochrome c are located in the particulate fraction of cells grown under high or low aeration, and both pigments are fully reducible by succinate. No evidence was found for the accumulation of the protein component of either cytochrome when synthesis of the prosthetic group was limited by Fe deficiency, nor did heme or precursors accumulate when protein synthesis was prevented. It was therefore concluded that the formation of the heme prosthetic group is closely integrated with the synthesis of the protein moiety. [delta]-Aminolevulinate synthase was detected in extracts of the organism. Its activity was correlated with cytochrome synthesis; it was reduced by high aeration and increased under low aeration. The synthase was inhibited by hemin at concentrations of 10 [mu]M or higher. The observations are consistent with a central role for the heme prosthetic group in the regulation of cytochrome synthesis.