title: Endogenous proteolysis of membrane-bound red cell cytochrome-b5 reductase in adults and newborns: its possible relevance to the generation of the soluble "methemoglobin reductase".
abstract: The problem of the low activity of so-called methemoglobin reductase in red cells from newborns was reinvestigated in view of our current knowledge of this enzyme, i.e., (1) its being cytochrome-b5 reductase and (2) its presence in two forms: soluble and membrane-bound. We found that red cells from cord blood and newborns exhibited a 50% decrease of soluble cytochrome-b5 reductase activity, whereas membrane-bound activity was in the adult range. Ghosts from these cells possessed diminished ability to solubilize membrane-bound cytochrome-b5 reductase in the course of in vitro auto-incubation. This autosolubilizing ability increased with age and reached adult level concomitantly with soluble cytochrome-b5 reductase activity at 6 mo. We conclude that the relative deficiency of soluble cytochrome-b5 reductase observed at birth is due to diminished post-translational processing of the membrane-bound enzyme during erythropoiesis of fetal cells. This processing is calcium-dependent related to calmodulin.
mesh_terms: D000328:Adult; D003579:Cytochrome Reductases / Q000378:metabolism*; D042966:Cytochrome-B(5) Reductase / Q000096:biosynthesis*; D004910:Erythrocyte Membrane / Q000201:enzymology*; D004912:Erythrocytes / Q000201:enzymology*; D005260:Female; D005312:Fetal Blood / Q000201:enzymology; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D008297:Male; D009247:NADH, NADPH Oxidoreductases / Q000096:biosynthesis*; D012995:Solubility
chemical_list: D009247:NADH, NADPH Oxidoreductases; D003579:Cytochrome Reductases; D042966:Cytochrome-B(5) Reductase