Question

Briefly describe (in words) the regulation of ribonucleotide reductase. Briefly, how is urea synthesis regulated?

Answer 1

RNRs are activated by binding ATP or inactivated by binding dATP to the activity site located on the RNR1 subunit. When the enzyme is activated, substrates are reduced if the corresponding effectors bind to the allosteric substrate specificity site.

Ribonucleotide reductase (RNR) converts ribonucleotides to deoxyribonucleotides, a reaction that is essential for DNA biosynthesis and repair. This enzyme is responsible for reducing all four ribonucleotide substrates, with specificity regulated by the binding of an effector to a distal allosteric site.

The biosynthesis of urea is regulated mainly by two factors, the amounts of urea cycleenzymes and the concentrations of acetyl-glutamate and ornithine. We reported that ornithine and acetylglutamate play a more important role in the regulation of urea synthesis especially shortly after the dietary change. The contents of all the urea cycle enzymes in the liver were directly proportional to the daily consumption of protein, then the activities of urea cycle enzymes are an important regulatory factor of the urea cycle.

The rate of urea synthesis from ammonium salt as a substrate were greatly changed in the perfused liver and correlated with the changes in the concentration of ornithine in the liver after the dietary changes.