Enzymes in intracellular organelles of adult and developing rat brain

Paul C. MacDonnell, Olga Greengard

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34 Scopus citations

Abstract

Eighty percent of the hexokinase and about a half of the lactate dehydrogenase, pyruvate kinase, and aldolase activities of adult rat cerebral homogenates is particulate, associated to a large extent, with the sediment (P2) obtained by centrifugation at 17,000g. Centrifugation of P2 into sucrose gradients shows that all four enzymes are associated with synaptosomes: their peak concentration coincides with that of glutamate decarboxylase rather than with those of mitochondrial enzymes, glutamate dehydrogenase, and aspartate aminotransferase. After hypoosmotic shock and high-speed centrifugation considerable portions of synaptosomal enzymes are recovered in the supernatant phase; the composition of this fluid, as indicated by the higher specific activity of several enzymes, is different from that of the soluble fraction of whole homogenates. The concentration of the seven enzymes studied is considerably lower in fetal than in adult brain and, in general, a larger fraction of the total is soluble. Preferential accumulation with age in the particulate fraction is especially striking in the case of hexokinase. Between fetal and adult life there are changes in the enzymic composition as well as increases in the amount of the total protein attributable to the synaptosomal fraction. Glutamate decarboxylase and lactate dehydrogenase are the synaptosomal enzymes to rise first (before or at birth), followed by hexokinase and, in the third postnatal week, by aldolase and pyruvate kinase. The upsurge of mitochondrial enzymes (that of glutamate dehydrogenase at term and of aspartate aminotransferase 10 days later) is accompanied by insignificant or small increases in the total protein content of the same fraction. The results indicate that the maturation of subcellular organelles involves a stepwise enrichment with various enzymes; some signs of biochemical differentiation precede and others coincide with the development of cerebral functions known to occur in 2- to 4-wk-old rats.

Original languageEnglish
Pages (from-to)644-655
Number of pages12
JournalArchives of Biochemistry and Biophysics
Volume163
Issue number2
DOIs
StatePublished - Aug 1974
Externally publishedYes

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