PURIFICATION AND CHARACTERIZATION OF CYSTATHIONINE BETA-LYASE FROM LACTOCOCCUS-LACTIS SUBSP, CREMORIS B78 AND ITS POSSIBLE ROLE IN FLAVOR DEVELOPMENT IN CHEESE

An enzyme that degrades sulfur-containing amino acids was purified fro m Lactococcus lactis subsp, cremoris B78; this strain was isolated fro m a mixed-strain, mesophilic starter culture used for the production o f Gouda cheese, The enzyme has features of a cystathionine P-lyase (EC 4.4.1.8), a pyridoxal-5'-phosphate-dependent enzyme involved in the b iosynthesis of methionine and catalyzing an alpha,beta-elimination rea ction, It is able to catalyze an alpha,gamma-elimination reaction as w ell, which in the case of methionine, results in the production of met hanethiol, a putative precursor of important flavor compounds in chees e, The native enzyme has a molecular mass of approximately 130 to 165 kDa and consists of four identical subunits of 35 to 40 kDa, The enzym e is relatively thermostable and has a pH optimum for activity around 8.0; it is still active under cheese-ripening conditions, viz., pH 5.2 to 5.4 and 4% (wt/vol) NaCl. A possible essential role of the enzyme in flavor development in cheese is suggested.