Purification and Characterization of l -Methionine γ-Lyase from Brevibacterium linens BL2

Abstract

L -Methionine γ-lyase (EC 4.4.1.11 ) was purified to homogeneity from Brevibacterium linens BL2, a coryneform bacterium which has been used successfully as an adjunct bacterium to improve the flavor of Cheddar cheese. The enzyme catalyzes the α,γ elimination of methionine to produce methanethiol, α-ketobutyrate, and ammonia. It is a pyridoxal phosphate-dependent enzyme, with a native molecular mass of approximately 170 kDa, consisting of four identical subunits of 43 kDa each. The purified enzyme had optimum activity at pH 7.5 and was stable at pHs ranging from 6.0 to 8.0 for 24 h. The pure enzyme had its highest activity at 25°C but was active between 5 and 50°C. Activity was inhibited by carbonyl reagents, completely inactivated by dl -propargylglycine, and unaffected by metal-chelating agents. The pure enzyme had catalytic properties similar to those of l -methionine γ-lyase from Pseudomonas putida . Its K _m for the catalysis of methionine was 6.12 mM, and its maximum rate of catalysis was 7.0 μmol min ⁻¹ mg ⁻¹ . The enzyme was active under salt and pH conditions found in ripening Cheddar cheese but susceptible to degradation by intracellular proteases.