?-Galactosidase and its significance in ripening mango fruit.
Ali Z. M., Armugam S., Lazan H.
Author Affiliation: Department of Biochemistry, Faculty of Life Sciences, Universiti Kebangsaan Malaysia, Bangi, 43600 Selangor, Malaysia.
Phytochemistry 38 : 1109-1114
Abstract : The extracts of ripening cv. Harumanis fruits contained a number of glycosidases and glycanases. Among the glycosidases, ?-galactosidase appeared to be the most significant. Enzyme activity increased in parallel with increasing fruit softness during ripening. Mango ?-galactosidase was fractioned into 3 isoforms (I, II and III) by a combination of chromatographic procedures on DEAE-Sepharose CL-6B, CM-Sepharose and Sephacryl S-200 columns. Apparent Km values for the respective isoforms for p-nitrophenyl ?-D-galactoside were 3.7, 3.3 and 2.7 mM, and their Vmax values were 209, 1024, and 62 nkat/mg protein. Optimum activity occurred at ca. pH 3.2 for ?-galactosidases I and II, and at pH 3.6 for ?-galactosidase III. Mango ?-galactosidase and its isoforms also exhibited galactanase activity; galactanase activity in the crude extracts generally increased during ripening. The close correlation between changes in ?-galactosidase activity, tissue softness, and increased pectin solubility and degradation suggests that ?-galactosidase might play an important role in cell wall pectin modification and softening of mango fruit during ripening.