ESR studies on reactivity of protein-derived tyrosyl radicals formed by prostaglandin H synthase and ribonucleotide reductase.
Using ESR spectroscopy, the ability of enzyme inhibitors to quench protein-derived tyrosyl radicals was studied in two different enzymes, prostaglandin H synthase and ribonucleotide reductase. The prostaglandin H synthase inhibitors indomethacin, eugenol, and MK-410 effectively prevent the formation of tyrosyl radicals during the oxidation of arachidonic acid by prostaglandin H synthase from ram seminal vesicles. A direct reaction with preformed tyrosyl radicals was observed only with eugenol. The other prostaglandin H synthase inhibitors were ineffective. The ribonucleotide reductase inhibitors hydroxyurea and 4-hydroxyanisole, which effectively inactivate the tyrosyl radical in the active site of ribonucleotide reductase present in tumor cells, exhibit a different reactivity with tyrosyl radicals formed by prostaglandin H synthase. Hydroxyurea quenches preformed tyrosyl radicals in prostaglandin H synthase weakly, whereas 4-hydroxyanisole does not quench tyrosyl radicals in prostaglandin H synthase at all. Eugenol, which quenches preformed prostaglandin H synthase-derived tyrosyl radicals, also quenches the tyrosyl radical in ribonucleotide reductase. The results suggest that the reactivity of protein-linked tyrosyl radicals in ribonucleotide reductase and those formed during prostaglandin H synthase catalysis are very different and have unrelated roles in enzyme catalysis.
Lassmann
G
G
Max-Delbrück-Center of Molecular Medicine, Berlin-Buch, Germany.
Curtis
J
J
Liermann
B
B
Mason
R P
RP
Eling
T E
TE
D000818:Animals; D000840:Anisoles / Q000494:pharmacology; D002286:Carcinoma, Ehrlich Tumor / Q000201:enzymology; D016861:Cyclooxygenase Inhibitors / Q000494:pharmacology*; D004578:Electron Spin Resonance Spectroscopy / Q000379:methods; D005054:Eugenol / Q000494:pharmacology; D005609:Free Radicals / Q000378:metabolism; D006918:Hydroxyurea / Q000494:pharmacology; D007210:Indoleacetic Acids / Q000494:pharmacology; D007213:Indomethacin / Q000494:pharmacology; D007700:Kinetics; D008297:Male; D051379:Mice; D011451:Prostaglandin-Endoperoxide Synthases / Q000737:chemistry / Q000378:metabolism*; D012264:Ribonucleotide Reductases / Q000737:chemistry / Q000378:metabolism*; D012669:Seminal Vesicles / Q000201:enzymology; D012756:Sheep; D014443:Tyrosine / Q000378:metabolism*
D000840:Anisoles; D016861:Cyclooxygenase Inhibitors; D005609:Free Radicals; D007210:Indoleacetic Acids; D005054:Eugenol; C079343:MK 410; D014443:Tyrosine; C009760:mequinol; D011451:Prostaglandin-Endoperoxide Synthases; D012264:Ribonucleotide Reductases; D006918:Hydroxyurea; D007213:Indomethacin