PURIFICATION AND PHYSICAL-PROPERTIES OF A NOVEL TYPE OF CYTOCHROME-B FROM RABBIT PERITONEAL NEUTROPHILS

The main redox component of the O-2(-) generating oxidase complex in n eutrophils is believed to be a b-type cytochrome, named cytochrome b(5 58). In the course of purification of cytochrome b(558) from rabbit pe ritoneal neutrophils, another hemoprotein with an apparent molecular m ass of 30 kDa, referred to as p-30, was isolated. Although the spectru m of p-30 was virtually identical to that of cytochrome b(558), its re dox potential, E(m7) = -4 +/- 10 mV, was much less negative than that of cytochrome b(558) (-270 +/- 5 mV). The alkaline pyridine hemochrome from purified p-30 was typical of a b-type cytochrome. The 20 N-termi nal amino acid residues and some tryptic peptides isolated from p-30 d id not show any significant sequence homology to the human phagocyte c ytochrome b(558) or to mitochondrial and microsomal cytochromes, excep t for the N-terminal region which displayed some homology to that of r at liver P-450. After subcellular fractionation, p-30 was found to be located in the plasma membrane and the granule fractions, similarly to cytochrome b(558). Upon neutrophil activation, part of p-30 was trans ferred from granules to the plasma membrane.