PURIFICATION AND CHARACTERIZATION OF L-METHIONINE GAMMA-LYASE FROM BREVIBACTERIUM LINENS BL2

L-Methionine gamma-lyase (EC 4.4.1.11) was purified to homogeneity fro m Brevibacterium linens BL2, a coryneform bacterium which has been use d successfully as an adjunct bacterium to improve the flavor of Chedda r cheese. The enzyme catalyzes the alpha,gamma elimination of methioni ne to produce methanethiol, alpha-ketobutyrate, and ammonia. It is a p yridoxal phosphate-dependent enzyme, with a native molecular mass of a pproximately 170 kDa, consisting of four identical subunits of 43 kDa each. The purified enzyme had optimum activity at pH 7.5 and was stabl e at pHs ranging from 6.0 to 8.0 for 24 h, The pure enzyme had its hig hest activity at 25 degrees C but was active between 5 and 50 degrees 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 gamma-lyase from Pseudomonas putida, Its K-m, for the catalysis of me thionine was 6.12 mM, and its maximum rate of catalysis was 7.0 mu mol min(-1) mg(-1). The enzyme was active under salt and pH conditions fo und in ripening Cheddar cheese but susceptible to degradation by intra cellular proteases.