Phosphorylation and modulation of the enzymic activity of native and protease-cleaved purified hepatic 3-hydroxy-3-methylglutaryl-coenzyme A reductase by a calcium/calmodulin-dependent protein kinase.

作者：Zafarul H. Beg, John A. Stonik, H Bryan Brewer · 发表于：Journal of Biological Chemistry · 年份：1987 · DOI：10.1016/s0021-9258(18)45191-5 · 被引用次数：44 · 研究领域：Enzyme Structure and Function、Protein Structure and Dynamics、Plant biochemistry and biosynthesis

A Ca2+/calmodulin-dependent kinase has been purified which catalyzed the phosphorylation and concomitant inactivation of both the microsomal native (100,000 Da) and protease-cleaved purified 3-hydroxy-3-methylglutaryl-coenzyme A reductase (HMG-CoA reductase) (53,000 Da) fragments. This low molecular weight brain cytosolic Ca2+/calmodulin-dependent kinase phosphorylates histone H1, synapsin I, and purified HMG-CoA reductase as major substrates. The kinase, purified by sequential chromatography on DEAE-cellulose, calmodulin affinity resin, and high performance liquid chromatography (TSKG 3000 SW) is an electrophoretically homogeneous protein of approximately 110,000 Da. The molecular weight of the holoenzyme, substrate specificity, subunit protein composition, subunit autophosphorylation, subunit isoelectric points, and subunit phosphopeptide analysis suggest that this kinase of Mr 110,000 may be different from other previously reported Ca2+/calmodulin-dependent kinases. Maximal phosphorylation by the low molecular form of Ca2+/calmodulin-dependent kinase of purified HMG-CoA reductase revealed a stoichiometry of approximately 0.5 mol of phosphate/mol of 53,000-Da enzyme. Dephosphorylation of phosphorylated and inactivated native and purified HMG-CoA reductase revealed a time-dependent loss of 32P-bound radioactivity and reactivation of enzyme activity. Based on the results reported here, we propose that HMG-CoA reductase activity may be modulated by yet another kinase system in...