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.