Question

Which of the following statements about the catalysis and regulation of Ribonucleotide Reductase (RNR) are Correct?

I. After product release, NADPH binds to RNR and reduces the disulfide bond formed in the α-subunit catalytic site during catalysis.

II. A free radical generated in the β-subunit is used to generate a free radical in the α-subunit active site nearly 35Å away.

III. When dATP concentrations are high enough, dATP binds to the RNR activity site and turns off the activity of RNR.

IV. The type of NDP substrate that binds to the RNR catalytic site is determined by the nucleotide bound at the RNR specificity site.

Choose the best answer

III and IV

I and II

II, III, and IV

II and III

I, II, and III

Answer 1

II,III and IV are correct.

In RNR regulation the free-radical in the beta subunit us responsible for the free radical generation in the alpha subunit. When dATP concentration are high the inhibit the activity of the RNR as they bind to the active site where it blocks it's original substrate to bind and progress the reaction. The binding of ATP nucleotide at the specificity sites of the RNR activates the enzyme. This can directly influence the type of NDP substance that bind to the catalytic site by changing the catalytic site structure.