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"
D Choury, A Reghis, AL Pichard and JC Kaplan
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.
Volume 61,
Issue 5,
pp. 894-898,
05/01/1983
Copyright © 1983 by The American Society of Hematology
