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Identification, Development, and Regional Distribution of Ribonucleotide Reductase in Adult Rat Brain
Author(s) -
Eells Janis Thane,
Spector Reynold
Publication year - 1983
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.1471-4159.1983.tb08085.x
Subject(s) - ribonucleotide reductase , ribonucleotide , specific activity , biochemistry , chemistry , enzyme , reductase , cytidine , enzyme assay , biology , nucleotide , protein subunit , gene
The development and regional distribution of ribonucleotide reductase (EC 1.17.4.1) were determined in rat brain. Ribonucleotide reductase was partially purified by ammonium sulfate fractionation (20‐40% saturation). Enzyme activity was measured by a specific radiochemical assay. This method involved the reduction of [ 14 C]cytidine diphosphate (CDP) to [ 14 C]deoxy‐cytidine diphosphate with subsequent hydrolysis and separation of the product ([ 14 C]deoxycytidine) from substrate ([ 14 C]cytidine) by Dowex‐1‐borate ion‐exchange chro‐matography. The specific activity of ribonucleotide reductase in whole brain of newborn rats was 3.78 ± 0.55 units (pmol/h)/mg protein (SEM; n = 6) and declined to 0.17 ± 0.01 units/mg protein (n = 7) at 10‐12 weeks of age, with a further decline to 0.11 ± 0.01 units/mg protein (n = 3) at 1 year. Ribonucleotide reductase activity in rat liver decreased from 4.58 ± 0.62 units/mg protein (n = 3) in newborn animals to 0.06 ± 0.01 units/mg protein (n = 7) at 10‐12 weeks and was present at trace levels at 6 months of age. The decline in specific activity with age was not due to a change in the K m for CDP. The K m for CDP in brain of newborn and adult rats was 80‐90 μM . In 10‐ to 12‐week‐old rats, the specific activity of ribonucleotide reductase was similar in the various regions of the brain tested except for the brainstem, which had 50% lower specific activity than the whole brain. These results indicate that ribonucleotide reductase activity is present and widely distributed in adult rat brain.