Properties and regulation of glutathione peroxidase.

GSH peroxidase has been purified approximately ZOO-fold from pig’s blood. With cumene hydroperoxide as substrate, kinetic analysis on the purified enzyme gave nonlinear Lineweaver-Burk plots for the hydroperoxide substrate. Linear Lineweaver-Burk plots were obtained for GSH and a limiting K, value of approximately 3 mu was obtained for GSH. A limited analysis of the rate data has been carried out and a tentative mechanism for GSH peroxidase is given. A wide range of nucleotides inhibited the enzyme, with pyrimidine nucleotides being the most effective. Also, the inhibitory effectiveness increased with the number of phosphate groups in the nucleotide. Nucleotide inhibition was competitive with respect to GSH whereas increased levels of hydroperoxide enhanced the inhibition. The sensitivity of the enzyme to nucleotide inhibition could be substantially decreased by x-ray, ethanol, or trypsin treatment, or aging with a lesser decrease of catalytic activity. Conversely, heat, p-chloromercuribenzoate, or sodium lauryl sulfate preferentially abolished the catalytic function with a lesser effect on the nucleotide response. It was concluded that nucleotides interact with the enzyme at a site other than the active center and hence that GSH peroxidase is an allosteric enzyme.