Cowles, Joe R.2022-07-292022-07-29197323155236https://hdl.handle.net/10657/10670Ribonucleotide reductase from Rhizobium meliloti was purified 8- to 10-fold, yielding a specific activity of 3250 nmoles dGDP formed/mg protein/hr. The optimum concentrations of dihydrolipoate, B[lowered 12] coenzyme, GDP and GTP were 20 mM, 30 uM, 0.2 mM and 1.6 mM, respectively. Although Mg[raised ++] and ATP were not required for enzyme activity as has been reported in other systems which reduce ribonucleoside diphosphates, these compounds did under certain conditions effect the rate of ribonucleotide reduction. In general, the addition of Mg[raised ++] at optimum GDP or GTP concentrations did not effect ribonucleotide reductase activity, whereas the addition of ATP was inhibitory. At one-half optimum substrate concentrations Mg[raised ++] and Mg[raised ++] plus ATP stimulated GDP and GTP reduction. When Ca[raised ++] was substituted for Mg[raised ++] essentially no effect was observed on reductase activity at optimum substrate concentrations; the substitution of Mn[raised ++] for Mg[raised ++] inhibited enzyme activity. At one-half optimum substrate concentrations, Ca[raised ++] stimulated enzyme activity, while Mn[raised ++] inhibited reductase activity slightly.application/pdfenThis item is protected by copyright but is made available here under a claim of fair use (17 U.S.C. Section 107) for non-profit research and educational purposes. Users of this work assume the responsibility for determining copyright status prior to reusing, publishing, or reproducing this item for purposes other than what is allowed by fair use or other copyright exemptions. Any reuse of this item in excess of fair use or other copyright exemptions requires express permission of the copyright holder.EnzymesThesisreformatted digital