Nature of cytochrome C reductase in nitrate reductase-deficient mutants in barley

Abstract

The nature of cytochrome c reductase (CR) in wild type and nitrate reductase-deficient nar mutants in barley (Hordeum vulgare L. cv Steptoe) was investigated. The activity of both the 4S and 8S CR species in the wild type and nar mutants was inhibited by nitrate reductase (NR) antiserum indicating that the 4S CR species was part of NR. The subunit molecular weight of both 4S and 8S CR species, determined by a combination of SDS-PAGE and immunolocalization (ELISA), was 110,000 thus demonstrating that the 4S CR species was the monomeric form of NR. The wild type and nar mutants with significant amounts of CR activity fall into two classes — one with CR mostly in the 8S form (Steptoe, nar 1d, nar 2a) and the other with most of the CR in the 4S form (nar 1b, nar 1g, nar 1i). These results support the notion that barley NR is a dimer with identical, 110 k Da subunits.