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-galactosidase (EC 3.2.1.23) appeared to be the most significant. The enzyme activity increased in parallel with increase in tissue softness during ripening. Mango beta-galactosidase was fractionated into three isoforms, viz. beta-galactosidase 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 beta-galactosidase isoforms for p-nitrophenyl beta-D-galactoside were 3.7, 3.3 and 2.7 mM, and their Vmax values were 209, 1024 and 62 nkat mg-1 protein. Optimum activity occurred at ca pH 3.2 for beta-galactosidase I and II, and pH 3.6 for beta-galactosidase III. Mango beta-galactosidase and its isoforms have galactanase activity, and the activity of the latter in the crude extracts generally increased during ripening. The close correlation between changes in beta-galactosidase activity, tissue softness, and increased pectin solubility and degradation suggests that beta-galactosidase might play an important role in cell wall pectin modification and softening of mango fruit during ripening.
Ali
Z M
ZM
Department of Biochemistry, Faculty of Life Sciences, Universiti Kebangsaan Malaysia, Selangor.
Armugam
S
S
Lazan
H
H
D002850:Chromatography, Gel; D002852:Chromatography, Ion Exchange; D005638:Fruit / Q000201:enzymology* / Q000254:growth & development; D006863:Hydrogen-Ion Concentration; D007527:Isoenzymes / Q000502:physiology*; D001616:beta-Galactosidase / Q000302:isolation & purification / Q000502:physiology*
D007527:Isoenzymes; D001616:beta-Galactosidase