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.
The hydroquinone and catechol like metabolites, NCQ344 and NCQ436 respectively, of the antipsychotic remoxipride have recently been demonstrated to induce apoptosis in myeloperoxidase (MPO)-rich human bone marrow progenitor and HL-60 cells [S.M. McGuinness, R. Johansson, J. Lundstrom, D. Ross, Induction of apoptosis by remoxipride metabolites in HL-60 and CD34+/CD19- human bone marrow progenitor cells: potential relevance to remoxipride-induced aplastic anemia, Chem. Biol. Interact. 121 (1999) 253-265]. In the present study, we determined the molecular mechanisms of apoptosis induced by these remoxipride metabolites in HL-60 cells. Our results show that apoptosis was accompanied by phosphatidylserine (PS) exposure, activation of caspases-9, -3, -7 and DNA cleavage. In HL-60 cells treated with the hydroquinone NCQ344 and catechol NCQ436, the general caspase inhibitor benzyloxycarbonyl-Val-Ala-Asp. fluoromethyl ketone (Z-VAD.FMK) blocked DNA cleavage and activation of caspases-9, -3/-7. In addition, PS exposure was significantly but not completely inhibited by Z-VAD.FMK. These results demonstrate that although Z-VAD.FMK inhibitable caspases are necessary for maximal apoptosis induced by NCQ344 and NCQ436, additional caspase-independent processes may orchestrate changes leading to PS exposure during apoptosis induced by the remoxipride polyphenolic metabolites.