BETA-GALACTOSIDASE AND ITS SIGNIFICANCE IN RIPENING MANGO FRUIT

The fruit extracts of ripening cv. Harumanis mango contained a number of glycosidases and glycanases. Among the glycosidases, beta-D-galacto sidase (EC 3.2.1.23) appeared to be the most significant. The enzyme a ctivity increased in parallel with increase in tissue softness during ripening. Mango beta-galactosidase was fractionated into three isoform s, viz. beta-galactosidase I, II and III by a combination of chromatog raphic procedures on DEAE-Sepharose CL-6B, CM-Sepharose and Sephacryl S-200 columns. Apparent K-m values for the respective beta-galactosida se isoforms for p-nitrophenyl beta-D-galactoside were 3.7, 3.3 and 2.7 mM, and their V-max values were 209, 1024 and 62 nkat mg(-1) protein. Optimum activity occurred at ca pH 3.2 for beta-galactosidase I and I I, and pH 3.6 for beta-galactosidase III. Mango beta-galactosidase and its isoforms have galactanase activity, and the activity of the latte r in the crude extracts generally increased during ripening. The close correlation between changes in beta-galactosidase activity, tissue so ftness, and increased pectin solubility and degradation suggests that beta-galactosidase might play an important role in cell wall pectin mo dification and softening of mango fruit during ripening.