Rhodopseudomonas capsulatarespiratory dehydrogenase mutants: An electron paramagnetic resonance study

Abstract

Rhodopseudomonas capsulata chromatophores derived from photosynthetically (malate) grown cells contain four ferredoxin-like centres detectable by electron paramagnetic resonance spectroscopy (EPR). These centres have EmT. 0 values of + 120, -115 , 2 8 0 and 3 7 0 mV (Zannoni and Ingledew, unpublished). In addition, a Rieskeand a HiPIP-type iron-sulphur centre are also detectable [1]. In this paper we report a study on the iron-sulphur centres in chromatophores derived from R. capsulata M-l, a mutant deficient in NADH-dehydrogenase activity, and from R. capsulata M-3, a mutant deficient in succinic dehydrogenase activity [2]. Chromatophores from the mutant M-1 contain only two ferredoxin centres, these with EmT. 0 of +120 and 2 8 0 mV. We ascribe these centres to the bacterial succinic dehydrogenase and relate the inability of M-1 chromatophores to perform NADH-dependent respiration to the lack of the ferredoxins with EmT. 0 at 3 7 0 and 1 1 5 mM. These latter centres are therefore tentatively ascribed to N A D H dehydrogenase. EPR studies on the mutant M-3 (succinate oxidase minus) gave an iron-sulphur centre profile similar to the wild-type chromatophores. We suggest that an inactive succinic dehydrogenase with a full complement of iron-sulphur clusters is produced in this mutant. 2.1. Cell growth, harvesting and breakage