The 3-O-glucosylation of steroidal sapogenins and alkaloids in eggplant (Solanum melongena); evidence for two separate glucosyltransferases
1998
Paczkowski, C. | Kalinowska, M. | Wojciechowski, Z.A.
UDP-glucose:diosgenin and UDP-glucose:solasodine glucosyltransferase are present in leaves, stems, roots and ripening seeds of garden eggplant (Solanum melongena). These two enzymes share several common properties: i) they occur mainly in the soluble proteins fraction; ii) they co-purify during purification procedure involving ammonium sulphate precipitation, ion-exchange chromatography on Q-Sepharose and gel filtration on Sephadex G-100; iii) they exhibit native M(r) values of ca 55 000; iv) they absolutely require reduced -SH groups; and v) they are strongly inhibited by some UDP-glucose analogues such as UDP. UDP-2',3'-dialdehyde and UDP-mannose. However, the above mentioned enzyme activities can be clearly distinguished using some other effectors. Low concentrations of several non-ionic detergents including Tween 80. Triton X-100 and Tyloxapol almost completely abolish glucosylation of diosgenin but have a slight stimulatory effect on glucosylation of solasodine. Synthetic diosgenin 3-O-beta-D-glucopyranoside strongly inhibits glucosylation of diosgenin and some related spirostanols but not that of solasodine. Cholesterol is a potent competitive inhibitor of diosgenin glucosylation (K(i)=1.15 micromolar) but it has little effect on the glucosylation rate of solasodine. The above data strongly suggest that 3-O-glucosylation of steroidal sapogenins and alkaloids in eggplant leaves is catalyzed by two similar though separate UDP-glucose-dependent glucosyltransferases.
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