Electron transport systems of Rhizobium japonicum. I. Haemoprotein P-450, other CO-reactive pigments, cytochromes and oxidases in bacteroids from N 2-fixing root nodules

Abstract

1. 1. This work characterizes some cytochromes, oxidases and CO-reactive pigments of Rhizobium japonicum bacteroids isolated from N 2-fixing soybean root nodules, and considers their functions in electron transfer or processes related to symbiotic nitrogen fixation. 2. 2. In common with cultured (non N 2-fixing) Rhizobia, bacteroids contain non-autoxidizable cytochrome c (550, Rhizobium) and cytochrome b. They lack the oxidases, cytochromes a− a 3 and o, found in cultured cells. Exclusively present in bacteroids are the soluble, autoxidizable CO-reactive pigments, cytochrome c (552, Rhizobium) and the haemoprotein P-450. Bacteroids also contain the pigments P-420 and P-428 tentatively identified by the major absorption peaks of their CO complexes. All pigments are biologically reducible and none appear to be artifacts. 3. 3. The succinate-oxidase pathway of aerobically-prepared bacteroids is inhibited by CN − and EDTA but not by CO; it may include a CN −-sensitive pigment with absorption peak (when reduced) at 502 nm.