COMPARATIVE STUDY OF EXTRACELLULAR AND INTRACELLULAR BETA-GLUCOSIDASES OF A NEW STRAIN OF ZYGOSACCHAROMYCES BAILII ISOLATED FROM FERMENTING AGAVE JUICE

摘要

A yeast strain isolated in the laboratory was studied and classified as a Zygosaccharomyces bailii. Both intracellular and extracellular beta-glucosidases of this yeast were purified by ion-exchange chromatography, gel filtration and hydroxylapatite (only for the intracellular enzyme). The tetrameric structure of the two beta-glucosidases was determined following treatment of the purified enzyme with dodecyl sulphate. The intracellular beta-glucosidase exhibited optimum activity at 65 degrees C and pH 5 . 5. The extracellular enzyme exhibited optimum catalytic activity at 55 degrees C and pH 5. The molecular mass of purified intracellular and extracellular beta-glucosidases, estimated by gel filtration, was 440 and 360 kDa, respectively. Both enzymes are active against glycosides with (1 --> 4)-beta, (1 --> 6)-beta and (1 --> 4)-alpha linkage configuration. The intracellular enzyme possesses (1 --> 6)-alpha-arabinofuranosidase activity and extracellular enzyme (1 --> 6)-alpha-rhamnopyranosidase activity. The two beta-glucosidases are competitively inhibited by glucose and by D-gluconic-acid-lactone and a slight glucosyl transferase activity is observed in the presence of ethanol. Since the glycosides present in wine and fruit juices represent a potential source of aromatic flavour, the possible use of the yeast beta-glucosidases for the liberation of the bound aroma is discussed.