The diurnal variation of hepatic HMG-CoA reductase activity is due to changes in the level of immunoreactive protein

The diurnal variation in levels of hepatic HMG-CoA reductase immunoreactive protein and enzyme activity were determined in rats. Immunoreactive protein levels changed together with enzyme activity. Thus the catalytic efficiency of HMG-CoA reductase was not significantly changed. The data suggest that the diurnal variation in hepatic HMG-CoA reductase activity is due to changes in enzyme protein levels rather than changes in phosphorylation state of the enzyme, for example, which would cause changes in catalytic efficiency. (C) 1996 Academic Press, Inc.