BETA-GLUCOSIDASE ACTIVITY IN FETAL BOVINE SERUM RENDERS THE PLANT GLUCOSIDE, HYPOXOSIDE, CYTOTOXIC TOWARD B16-F10-BL-6 MOUSE MELANOMA-CELLS

By using rho-nitrophenyl-beta-D-glucopylanoside as substrate, beta-glu cosidase activity was observed in fetal bovine serum (FBS). This activ ity could be inhibited by heat inactivation of the serum. Gel chromato graphy of FBS indicated the presence of beta-glucosidase activity with an apparent molecular mass of 29 kDa. In McCoy's 5A medium supplement ed with non-heat inactivated FBS, the diglucoside hypoxoside lucopyran osyloxy-3'-hydroxyphenyl]pent-4-en-1-yne) showed cytotoxicity toward B 16-F10-BL-6 mouse melanoma cells. In incubations where the media were supplemented with FBS previously heat inactivated at 56 degrees C for 1 h or more, no cytotoxicity was observed in the presence of hypoxosid e. The aglucone of hypoxoside, rooperol ([E]-1,5-bis[3'4'-dihydroxyphe nyl]pent-4-en-1-yne showed cytotoxic- regardless of whether the serum was heat inactivated or not. The kinetics of the heat inactivation of the beta-glucosidase activity in FBS coincided with the loss of appare nt cytotoxicity of hypoxoside. High performance liquid chromatography analysis showed that rooperol could be generated by incubation of hypo xoside in non-heat inactivated FBS, but that this ability was lost in serum that was heat inactivated for 1 h or longer. Newborn bovine seru m did not contain any beta-glucosidase activity whereas it was found i n three different commercial sources of FBS. This observation is of pr actical importance because conventional heat inactivation of FBS at 56 degrees C for 30 min was not sufficient to inactivate the beta-glucos idase activity completely.