Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:2.7.11.1 (protein kinase)
 81,284 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The activity of rat liver 3-hydroxy-3-methylglutaryl-coenzyme A reductase [HMG-CoA reductase; mevalonate:NADP(+) oxidoreductase (CoA-acylating), EC 1.1.1.34] can be modulated in vitro by a phosphorylation-dephosphorylation reaction sequence. A microsomal reductase kinase catalyzes the phosphorylation of HMG-CoA reductase and histones. Histone phosphorylation was enhanced 2- to 3-fold by cyclic AMP. Reductase kinase exists in interconvertible active and inactive forms. Incubation of reductase kinase with phosphoprotein phosphatase resulted in a time-dependent decrease in the ability of reductase kinase to catalyze the phosphorylation of histones and to inactivate HMG-CoA reductase. Incubation of phosphoprotein phosphatase-inactivated reductase kinase with [gamma-(32)P]ATP plus Mg(2+) and a partially purified protein kinase designated reductase kinase kinase resulted in parallel increases in protein-bound (32)P radioactivity and ability to inactivate HMG-CoA reductase. Incubation of (32)P-labeled reductase kinase with phosphoprotein phosphatase resulted in a time-dependent loss of protein-bound (32)P radioactivity and a decrease in the ability to inactivate HMG-CoA reductase. Polyacrylamide gel electrophoresis of purified reductase kinase incubated with reductase kinase kinase and [gamma-(32)P]ATP plus Mg(2+) revealed that the (32)P radioactivity and reductase kinase enzymic activity were located in a single electrophoretic position. Dephosphorylation of (32)P-labeled purified reductase kinase with phosphoprotein phosphatase was associated with significant loss of radioactivity and enzymic activity in the protein band ascribed to reductase kinase. These results provide evidence that the activity of reductase kinase, like HMG-CoA reductase, is modulated by a reversible phosphorylation-dephosphorylation reaction sequence.
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PMID:Characterization and regulation of reductase kinase, a protein kinase that modulates the enzymic activity of 3-hydroxy-3-methylglutaryl-coenzyme A reductase. 29 71

Cyclic AMP has been implicated to a greater or lesser extent in the regulation of four key enzymes which interact to regulate intracellular cholesterol metabolism; HMG CoA reductase; ACAT; cholesteryl ester hydrolase; and cholesterol 7 alpha hydroxylase. The relationship between these enzymes and the sites where current evidence suggests that cyclic AMP may be involved are summarized in Fig. 3. Cholesterol 7 alpha hydroxylase controls the catabolism of cholesterol to bile acids in the liver, and thus its removal from the body via the bile, but does not have a major role in cholesterol metabolism in extrahepatic tissues. It is clear that cyclic AMP is able to influence the activity of this enzyme in liver sub-cellular fractions and isolated hepatocytes in vitro, and studies in our laboratory have shown that changes in Ca2+ fluxes within the cell may be important in its mechanism of action. Whether or not the cyclic nucleotide has a role regulating cholesterol 7 alpha hydroxylase activity in vivo, however, is not known. HMG CoA reductase is inactivated by phosphorylation both in vitro and in vivo, but although cyclic AMP and glucagon have been shown to inhibit the enzyme, cyclic AMP-dependent protein kinase is not directly involved. The exact mechanism by which the cyclic nucleotide influences the system remains unclear, but it may be related to activation of microsomal phosphatases. The activity of ACAT has been shown to be modulated by phosphorylation in a number of tissues in vitro, but the involvement of cyclic AMP has not been unequivocally demonstrated.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Cyclic AMP and the regulation of cholesterol metabolism. 132 21

Protein phosphorylation is well established as a regulatory mechanism in higher plants, but only a handful of plant enzymes are known to be regulated in this manner, and relatively few plant protein kinases have been characterized. AMP-activated protein kinase regulates key enzymes of mammalian fatty acid, sterol and isoprenoid metabolism, including 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase. We now show that there is an activity in higher plants which, by functional criteria, is a homologue of the AMP-activated protein kinase, although it is not regulated by AMP. The plant kinase inactivates mammalian HMG-CoA reductase and acetyl-CoA carboxylase, and peptide mapping suggests that it phosphorylates the same sites on these proteins as the mammalian kinase. However, with the target enzymes purified from plant sources, it inactivates HMG-CoA reductase but not acetyl-CoA carboxylase. The kinase is located in the soluble, and not the chloroplast, fraction of leaf cells, consistent with the idea that it regulates HMG-CoA reductase, and hence isoprenoid biosynthesis, in vivo. The plant kinase also appears to be part of a protein kinase cascade which has been highly conserved during evolution, since the kinase is inactivated and reactivated by mammalian protein phosphatases (2A or 2C) and mammalian kinase kinase, respectively. This contrasts with the situation for many other mammalian protein kinases involved in signal transduction, which appear to have no close homologue in higher plants. To our knowledge, this represents the first direct evidence for a protein kinase cascade in higher plants.
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PMID:Evidence for a protein kinase cascade in higher plants. 3-Hydroxy-3-methylglutaryl-CoA reductase kinase. 135 11

Adrenalin and glucagon inhibit glycogen, fatty acid and cholesterol synthesis by elevation of cyclic AMP, activation of cyclic AMP-dependent protein kinase and increased phosphorylation of the rate-limiting enzymes of these pathways. Here, we review recent evidence which indicates that inhibition of these biosynthetic pathways in muscle, adipose tissue and liver is much more indirect than has previously been supposed. In particular, cyclic AMP-dependent protein kinase does not appear to inhibit glycogen synthase, acetyl-CoA carboxylase and HMG-CoA reductase by phosphorylating them directly. It appears to achieve the same end result by inactivation of the protein phosphatases which dephosphorylate these regulatory enzymes in vivo, although this has only been established definitively in the case of glycogen synthesis.
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PMID:The actions of cyclic AMP on biosynthetic processes are mediated indirectly by cyclic AMP-dependent protein kinase. 165 40

The primary structure of bovine rhodopsin kinase (RK), which phosphorylates light-activated rhodopsin (Rho*), terminates with the amino acid sequence Cys558-Val-Leu-Ser561, a motif that has been shown to direct the isoprenylation and alpha-carboxyl methylation of many proteins (e.g. p21Ha-ras). Transient expression of RK in COS-7 cells revealed the presence of two immunoreactive protein species. Consistent with RK being modified by isoprenylation, interconversion of these two species was dependent upon isoprenoid biosynthesis in the cells. Moreover, a serine substitution for Cys558 resulted in a single RK species whose migration on sodium dodecyl sulfate-polyacrylamide gels was identical to that of RK from cells treated with mevinolin, an inhibitor of 3-hydroxy-3-methylglutaryl-coenzyme A reductase and, thus, of isoprenoid biosynthesis. This finding indicates that isoprenylation of RK requires Cys558. The electrophoretic mobility of isoprenylated RK synthesized in COS-7 cells was identical to that of RK from bovine rod outer segments, suggesting that RK is isoprenylated in vivo. RK was determined to be modified by a farnesyl moiety and alpha-carboxyl-methylated. A time course of Rho* phosphorylation revealed that non-processed RK is approximately 4-fold less active than wild-type RK. This is the first demonstration of isoprenylation/alpha-carboxyl methylation of a protein kinase, and suggests that these modifications markedly influence enzymatic activity in vivo.
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PMID:Isoprenylation of a protein kinase. Requirement of farnesylation/alpha-carboxyl methylation for full enzymatic activity of rhodopsin kinase. 173 Jun 92

Several rat liver HMG-CoA-reductase (HMG-CoA-Rd) phosphatase activities have been shown to be associated with the endoplasmic reticulum. These activities were not due to glycogen contamination, as judged not only from different patterns of solubilization of the microsomal membranes and the glycogen pellet but also by differential centrifugation behavior under standard conditions and in a sucrose gradient. We present evidence that at least three forms of protein phosphatase are associated with microsomal membranes: a polycation-stimulated type 2A phosphatase, a type 2C phosphatase, and a non-2A, non-2B, non-2C phosphatase. This last HMG-CoA-Rd phosphatase activity corresponding to an 85 kDa protein was partially purified by several chromatographic procedures. The IC50 value for the inhibition of the HMG-CoA-Rd phosphatase by I-2 was 10-fold higher than for the inhibition of the purified type 1 catalytic subunit from rabbit skeletal muscle. The microsomal HMG-CoA-Rd phosphatase activity was slightly affected by the protein inhibitor that inhibits type 2A activity when HMG-CoA reductase is the substrate. The HMG-CoA-Rd phosphatase activity is spontaneously active and it is not reactivated in the presence of Mg2+ or polycations. The holoenzyme does not contain the inhibitor-2 and it is not reactivated by incubation with ATP and glycogen synthase kinase-3. Proteolytic treatment of the enzyme yielded a polypeptide fragment of low Mr (37 kDa) with reduced activity. A model of holoenzymatic HMG-CoA-Rd phosphatase and its relation to the microsomal membranes is presented.
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PMID:Isolation and partial characterization of a protein with HMG-CoA reductase phosphatase activity associated with rat liver microsomal membranes. 175 9

A protein inhibitor of HMG-CoA reductase phosphatase activity from rat liver was purified to homogeneity. The protein was purified 4,000-fold with an overall yield of 4%. The purified protein had a molecular mass of 31 kDa. This spontaneously active protein is thermostable and acid-resistant. The protein inhibitor is phosphorylated by glycogen synthase kinase-3 and cAMP-dependent protein kinase without change in its inhibitory activity. The inhibition caused by this inhibitor on phosphatases 1 and 2A is similar to that of inhibitor-2 from rabbit skeletal muscle using hydroxymethylglutaryl-CoA reductase as substrate. The regulation properties of this inhibitor towards phosphatase 1 together with another protein inhibitor of phosphatase 2A in cholesterol metabolism are discussed.
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PMID:Purification and characterization of a protein inhibitor from rat liver that inhibits type 1 protein phosphatase when 3-hydroxy-3-methylglutaryl CoA reductase is the substrate. 216 23

Calmodulin-dependent multiprotein kinase and protein kinase C phosphorylate and inactivate both intact, microsomal HMG-CoA reductase, and the purified 53 kDa catalytic fragment. Isolation of the single phosphopeptide produced by combined cleavage with cyanogen bromide and Lys-C proteinase reveals that this is due to phosphorylation of a single serine residue near the C-terminus, corresponding to serine-872 in the human enzyme. This is identical with the single serine phosphorylated by the AMP-activated protein kinase. The nature of the protein kinase responsible for phosphorylation of this site in vivo is discussed.
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PMID:Calmodulin-dependent multiprotein kinase and protein kinase C phosphorylate the same site on HMG-CoA reductase as the AMP-activated protein kinase. 238 4

A heat-stable protein inhibitor of the hydroxymethylglutaryl-CoA reductase phosphatase 2A activity has been identified and purified to homogeneity, as judged by polyacrylamide gel electrophoresis. The apparent molecular mass was 20,000 Da. The protein lost its inhibitory properties when incubated with trypsin or treated with ethanol. The inhibitor protein does not inhibit type 1 phosphatase when either phosphorylase or hydroxymethylglutaryl-CoA reductase is the substrate. In contrast, this protein inhibitor inhibits the rat liver type 2A phosphatase activity when hydroxymethylglutaryl-CoA reductase is the substrate but not when phosphorylase a is the substrate. The inhibitor protein is not activated by incubation with ATP and cyclic AMP-dependent protein kinase and it is not phosphorylated by glycogen synthase kinase-3. These results, together with those of the kinetic experiments, suggest that the reductase phosphatase inhibitor is distinct from protein phosphatase inhibitor-1 and inhibitor-2.
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PMID:Purification and properties of a protein inhibitor that inhibits phosphatase 2A activity when hydroxymethylglutaryl coenzyme A reductase is the substrate. 254 29

In addition to acetyl-CoA carboxylase and HMG-CoA reductase, the AMP-activated protein kinase phosphorylates glycogen synthase, phosphorylase kinase, hormone-sensitive lipase and casein. A number of other substrates for the cyclic AMP-dependent protein kinase, e.g., L-pyruvate kinase and 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase, are not phosphorylated at significant rates. Examination of the sites phosphorylated on acetyl-CoA carboxylase, hormone-sensitive lipase, glycogen synthase and phosphorylase kinase suggests a consensus recognition sequence in which the serine residue phosphorylated by the AMP-activated protein kinase has a hydrophobic residue on the N-terminal side (i.e., at -1) and at least one arginine residue at -2, -3 or -4. Substrates for cyclic AMP-dependent protein kinase which lack the hydrophobic residue at -1 are not substrates for the AMP-activated protein kinase.
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PMID:The substrate and sequence specificity of the AMP-activated protein kinase. Phosphorylation of glycogen synthase and phosphorylase kinase. 256 85


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