Eells J T, Spector R
J Neurochem. 1983 Apr;40(4):1008-12. doi: 10.1111/j.1471-4159.1983.tb08085.x.
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 [14C]cytidine diphosphate (CDP) to [14C]deoxycytidine diphosphate with subsequent hydrolysis and separation of the product ([14C]deoxycytidine) from substrate ([14C]cytidine) by Dowex-1-borate ion-exchange chromatography. 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 Km for CDP. The Km for CDP in brain of newborn and adult rats was 80-90 microM. 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.
