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DEVELOPMENTAL CHANGES IN THE DISTRIBUTION OF 3‐HYDROXY‐3‐METHYLGLUTARYL COENZYME A REDUCTASE AMONG SUBCELLULAR FRACTIONS OF RAT BRAIN 1
Author(s) -
MALTESE WILLIAM A.,
VoLPE JOSEPH J.
Publication year - 1979
Publication title -
journal of neurochemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.75
H-Index - 229
eISSN - 1471-4159
pISSN - 0022-3042
DOI - 10.1111/j.1471-4159.1979.tb11712.x
Subject(s) - reductase , microsome , 7 dehydrocholesterol reductase , hydroxymethylglutaryl coa reductase , coenzyme a , biochemistry , endoplasmic reticulum , hmg coa reductase , differential centrifugation , biology , cell fractionation , enzyme
—The distribution of 3‐hydroxy‐3‐methylglutaryl coenzyme A (HMG‐CoA) reductase (EC 1.1.1.34) relative to that of several biochemical markers has been studied in subcellular fractions prepared from the brains of rats, aged 4 days to adult, by differential centrifugation. In the brains of 10‐day‐old animals fractions which sedimented at 800 g (P 1 and 9000 g (P 2 ) contained 28% and 65% respectively of the total reductase activity. A similar distribulion of the microsomal marker, NADPH‐cytochrome c reductase, suggested that the HMG‐CoA reductase activity in the low‐speed pellets was due to substantial contamination of these fractions with endoplasmic reticulum. When P 2 was fractionated on a discontinuous sucrose gradient, the distributions of protein, RNA and NADPH‐cytochrome c reductase paralleled that of HMG‐CoA reductase, indicaling a non‐specific association of endoplasmic reliculum and HMG‐CoA reductase with all of the structures sedimenting in P 2 . As brain maturation proceeded and a greater percentage of total brain protein (primarily associated with myelin) sedimenled in P 1 , the subcellular distributions of HMG‐CoA reductase and the microsomal marker changed in a parallel way. By 21 days P 1 contained nearly all of the reductase activity. Because the specific activity of HMG‐CoA reductase in P 1 decreased steadily between 4 and 21 days, while the specific activity of 2′:3′‐cyclic nucleotide 3′‐phosphohydrolase in this fraction increased in a coordinate fashion, we conclude that the reductase is not an integral component of myelin, and probably is associated exclusively with the endoplasmic reticulum included in P 1 . In view of the developmental changes in the distribution of HMG‐CoA reductase among subcellular fraclions, we suggest that whole homogenates (or comparable tissue extracts) should be utilized to evaluate reductase activity in the developing brain.