Binding of substrates to Escherichia coli ribonucleotide reductase.

摘要: Ribonucleoside diphosphate reductase from Escherichia coli consists of a 1/1 complex two nonidentical subunits called proteins B1 and B2. The enzyme reduces the four common ribonucleoside diphosphates to corresponding deoxyribonucleotides is allosterically regulated by nucleoside triphosphates which influence its substrate specificity as well overall activity. subunit contains binding sites for effectors while B2 iron an organic free radical essential catalytic We now establish that only protein binds substrates. Competition experiments support presence identical sites, distinct effector sites. site thus formed both subunits. Dissociation constants substrates ranged 2 X 10(-5) about 10(-3) M. In all cases decreased these in agreement with their on ribonucleotide reductase, but did not induce cooperative effects. increase was pronounced at 20 degrees marginal 0 degrees. Arrhenius plots temperature activity showed sharp breaks 12 effects can be interpreted conformational change occurring structure critical temperature.