Journal of Lipid Research, Vol 21, 399-405, Copyright © 1980 by Lipid Research, Inc.
Regulation of vertebrate liver HMG-CoA reductase via reversible modulation of its catalytic activity
CF Hunter and VW Rodwell
We have investigated the comparative biochemistry of in vitro regulation of
HMG-CoA reductase (EC 1.1.1.34) in microsomal preparations from the livers
of nine vertebrates. In all instances, reductase activity was rapidly and
profoundly decreased by addition of MgATP. Reductase activities were
restored to near or above initial levels after removal of MgATP and
incubation with a crude, low molecular weight phosphatase preparation from
rat liver cytosol. Restoration of reductase activity was inhibited both by
NaF and by pyrophosphate, known inhibitors of phosphoprotein phosphatase
activity. Liver cytosol of species other than the rat exhibits reductase
phosphatase activity. The converter enzymes that catalyze modulation of
MG-CoA reductase activity (reductase kinase and reductase phosphatase) thus
appear to be ubiquitous in vertebrate liver. Interconversion in vitro of
active and inactive forms of reductase probably is general for vertebrate
liver also. The majority of the reductase present in vertebrate liver may
be present in a catalytically inactive or latent form in vivo. Under the
experimental conditions used, the fraction present in the active form is,
for a given species, quite constant. Species to species, from 20-45% of the
reductase appears to be present in the active form.
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