PURIFICATION AND CHARACTERIZATION OF CYSTATHIONINE GAMMA-LYASE FROM LACTOCOCCUS-LACTIS SUBSP CREMORIS SK11 - POSSIBLE ROLE IN FLAVOR COMPOUND FORMATION DURING CHEESE MATURATION

A cystathionine gamma-lyase (EC 4.4.1.1.) (gamma-CTL) was purified to homogeneity from a crude cell extract of Lactococcus lactis subsp, cre moris SK11 by a procedure including anion-exchange chromatography, hyd rophobic interaction chromatography, and gel filtration chromatography . The activity of SK11 gamma-CTL is pyridoxal-5'-phosphate dependent, and the enzyme catalyzes the alpha,gamma-elimination reaction of L-cys tathionine to produce L-cysteine, alpha-ketobutyrate, and ammonia, The native enzyme has a molecular mass of approximately 120 to 200 kDa an d apparently consists of at least six identical subunits of 20 kDa, In this respect, the SK11 enzyme clearly differs from other bacterial cy stathionine lyases, which are all tetrameric proteins with identical s ubunits of approximately 40 kDa, In addition, the specific activity of purified SK11 gamma-CTL toward L-cystathionine is relatively low comp ared with those reported for other bacterial cystathionine lyases, The SK11 enzyme shows a broad substrate specificity, In the case of L-met hionine, the action of SK11 gamma-CTL results in the formation of meth anethiol, a volatile sulfur compound known to be required in flavor de velopment in cheddar cheese, The alpha,beta-elimination reaction of L- cysteine is also efficiently catalyzed by the enzyme, resulting in the formation of hydrogen sulfide, Although the conditions are far from o ptimal, cystathionine gamma-lyase is still active under cheddar cheese -ripening conditions, namely, pH 5.0 to 5.4 and 5% (wt/vol) NaCl, The possible role of the enzyme in cheese flavor development is discussed.