Phosphorylation state of HMG CoA reductase affects its catalytic activity and degradation

Rex A. Parker, Steven Miller, David M. Gibson

Research output: Contribution to journalArticle

3 Citations (Scopus)

Abstract

The expressed catalytic activity of liver microsomal HMG CoA reductase, the limiting enzyme in cholesterol synthesis, is reversibly diminished by phosphorylation in vitro. In intact hepatocytes the expressed activity of HMG CoA reductase is enhanced by incubation of cells with insulin, and diminished by treatment with glucagon or with mevalonate. In the latter situations the level of total reductase activity falls following initial inactivation (phosphorylation) of the enzyme. This observation suggested that the phosphorylated form of HMG CoA reductase is more sensitive to proteolysis. HMG CoA reductase is a 97,000 dalton (97 K) integral protein of the endoplasmic reticulum with a cytosolic domain that includes the catalytic site and serine residues that may be reversibly phosphorylated. In vitro the Ca2+-activated proteolytic enzyme, calpain, generates two catalytically-active fragments: a membrane bound 62 K and a soluble 53 K form of the enzyme which are quantified by specific immunoblot procedures. Cleavage of the native 97 K HMG CoA reductase is enhanced by pretreatment (inactivation) of microsomes with ATP (Mg2+) and liver reductase kinase compared to microsomes pretreated with protein phosphatase. This is reflected in a loss of 97 K reductase and an increase in the soluble 53 K form of the enzyme. Degradation of HMG CoA reductase in hepatocytes is partially blocked by lysosomotropic agents and insulin. A steady state model for the turnover of proteins subject to reversible phosphorylation has been developed which recognizes fractional degradative rate constants for the phosphorylated and dephosphorylated species.

Original languageEnglish
Pages (from-to)329-343
Number of pages15
JournalAdvances in Enzyme Regulation
Volume25
Issue numberC
DOIs
StatePublished - 1986

Fingerprint

Hydroxymethylglutaryl CoA Reductases
Phosphorylation
Catalyst activity
Degradation
Oxidoreductases
Enzymes
Microsomes
Liver
Hepatocytes
Insulin
Proteolysis
Mevalonic Acid
Calpain
Phosphoprotein Phosphatases
Glucagon
Endoplasmic Reticulum
Serine
Rate constants
Catalytic Domain
Proteins

ASJC Scopus subject areas

  • Biochemistry
  • Molecular Biology

Cite this

Phosphorylation state of HMG CoA reductase affects its catalytic activity and degradation. / Parker, Rex A.; Miller, Steven; Gibson, David M.

In: Advances in Enzyme Regulation, Vol. 25, No. C, 1986, p. 329-343.

Research output: Contribution to journalArticle

@article{1b95b87e9ad14bd79d239cf3ccc0a9fa,
title = "Phosphorylation state of HMG CoA reductase affects its catalytic activity and degradation",
abstract = "The expressed catalytic activity of liver microsomal HMG CoA reductase, the limiting enzyme in cholesterol synthesis, is reversibly diminished by phosphorylation in vitro. In intact hepatocytes the expressed activity of HMG CoA reductase is enhanced by incubation of cells with insulin, and diminished by treatment with glucagon or with mevalonate. In the latter situations the level of total reductase activity falls following initial inactivation (phosphorylation) of the enzyme. This observation suggested that the phosphorylated form of HMG CoA reductase is more sensitive to proteolysis. HMG CoA reductase is a 97,000 dalton (97 K) integral protein of the endoplasmic reticulum with a cytosolic domain that includes the catalytic site and serine residues that may be reversibly phosphorylated. In vitro the Ca2+-activated proteolytic enzyme, calpain, generates two catalytically-active fragments: a membrane bound 62 K and a soluble 53 K form of the enzyme which are quantified by specific immunoblot procedures. Cleavage of the native 97 K HMG CoA reductase is enhanced by pretreatment (inactivation) of microsomes with ATP (Mg2+) and liver reductase kinase compared to microsomes pretreated with protein phosphatase. This is reflected in a loss of 97 K reductase and an increase in the soluble 53 K form of the enzyme. Degradation of HMG CoA reductase in hepatocytes is partially blocked by lysosomotropic agents and insulin. A steady state model for the turnover of proteins subject to reversible phosphorylation has been developed which recognizes fractional degradative rate constants for the phosphorylated and dephosphorylated species.",
author = "Parker, {Rex A.} and Steven Miller and Gibson, {David M.}",
year = "1986",
doi = "10.1016/0065-2571(86)90022-1",
language = "English",
volume = "25",
pages = "329--343",
journal = "Advances in Biological Regulation",
issn = "2212-4926",
publisher = "Elsevier BV",
number = "C",

}

TY - JOUR

T1 - Phosphorylation state of HMG CoA reductase affects its catalytic activity and degradation

AU - Parker, Rex A.

AU - Miller, Steven

AU - Gibson, David M.

PY - 1986

Y1 - 1986

N2 - The expressed catalytic activity of liver microsomal HMG CoA reductase, the limiting enzyme in cholesterol synthesis, is reversibly diminished by phosphorylation in vitro. In intact hepatocytes the expressed activity of HMG CoA reductase is enhanced by incubation of cells with insulin, and diminished by treatment with glucagon or with mevalonate. In the latter situations the level of total reductase activity falls following initial inactivation (phosphorylation) of the enzyme. This observation suggested that the phosphorylated form of HMG CoA reductase is more sensitive to proteolysis. HMG CoA reductase is a 97,000 dalton (97 K) integral protein of the endoplasmic reticulum with a cytosolic domain that includes the catalytic site and serine residues that may be reversibly phosphorylated. In vitro the Ca2+-activated proteolytic enzyme, calpain, generates two catalytically-active fragments: a membrane bound 62 K and a soluble 53 K form of the enzyme which are quantified by specific immunoblot procedures. Cleavage of the native 97 K HMG CoA reductase is enhanced by pretreatment (inactivation) of microsomes with ATP (Mg2+) and liver reductase kinase compared to microsomes pretreated with protein phosphatase. This is reflected in a loss of 97 K reductase and an increase in the soluble 53 K form of the enzyme. Degradation of HMG CoA reductase in hepatocytes is partially blocked by lysosomotropic agents and insulin. A steady state model for the turnover of proteins subject to reversible phosphorylation has been developed which recognizes fractional degradative rate constants for the phosphorylated and dephosphorylated species.

AB - The expressed catalytic activity of liver microsomal HMG CoA reductase, the limiting enzyme in cholesterol synthesis, is reversibly diminished by phosphorylation in vitro. In intact hepatocytes the expressed activity of HMG CoA reductase is enhanced by incubation of cells with insulin, and diminished by treatment with glucagon or with mevalonate. In the latter situations the level of total reductase activity falls following initial inactivation (phosphorylation) of the enzyme. This observation suggested that the phosphorylated form of HMG CoA reductase is more sensitive to proteolysis. HMG CoA reductase is a 97,000 dalton (97 K) integral protein of the endoplasmic reticulum with a cytosolic domain that includes the catalytic site and serine residues that may be reversibly phosphorylated. In vitro the Ca2+-activated proteolytic enzyme, calpain, generates two catalytically-active fragments: a membrane bound 62 K and a soluble 53 K form of the enzyme which are quantified by specific immunoblot procedures. Cleavage of the native 97 K HMG CoA reductase is enhanced by pretreatment (inactivation) of microsomes with ATP (Mg2+) and liver reductase kinase compared to microsomes pretreated with protein phosphatase. This is reflected in a loss of 97 K reductase and an increase in the soluble 53 K form of the enzyme. Degradation of HMG CoA reductase in hepatocytes is partially blocked by lysosomotropic agents and insulin. A steady state model for the turnover of proteins subject to reversible phosphorylation has been developed which recognizes fractional degradative rate constants for the phosphorylated and dephosphorylated species.

UR - http://www.scopus.com/inward/record.url?scp=0023016351&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=0023016351&partnerID=8YFLogxK

U2 - 10.1016/0065-2571(86)90022-1

DO - 10.1016/0065-2571(86)90022-1

M3 - Article

C2 - 3028050

AN - SCOPUS:0023016351

VL - 25

SP - 329

EP - 343

JO - Advances in Biological Regulation

JF - Advances in Biological Regulation

SN - 2212-4926

IS - C

ER -