CATALYTIC ACTION OF L-METHIONINE GAMMA-LYASE ON SELENOMETHIONINE AND SELENOLS

We examined the catalytic action of l-methionine γ-lyase (EC 4.4.1.11) on selenomethionine (2-amino-4-(methylseleno)butyric acid), methaneselenol, 1-hexaneselenol, and benzeneselenol. The enzyme catalyzes α,γ-elimination of selenomethionine to yield α-ketobutyrate, ammonia, and methaneselenol, and also its γ-replacement reaction with various thiols to produce S-substituted homocysteines. Selenomethionine is an even better substrate than methionine in α,γ-elimination but is less effective in γ-replacement.In addition, l-methionine γ-lyase catalyzes γ-replacement reaction of methionine and its derivatives with selenols to form the corresponding Se-substituted selenohomocysteines, although selenols are less efficient substituent donors than thiols. This is the first proven mechanism for the incorporation of selenium atom into amino acids. © 1979, American Chemical Society. All rights reserved.