GLUCOSYLATION OF C-19-HYDROXYSTEROID AND C-21-HYDROXYSTEROID BY SOLUBLE AND MEMBRANE-BOUND GLUCOSYLTRANSFERASE FROM OAT (AVENA-SATIVA) SEEDLINGS

Several 3 beta-hydroxy derivatives of pregnane or androstane, containing a planar ring system (5 alpha-H or Delta(5)), e.g. pregnenolone, epiandrosterone and dehydroisoandrosterone, are readily glucosylated by delipidated enzyme preparations from oat seedlings in the presence of UDPGlc. Two different glucosyl transferases are involved in these reactions: a soluble (cytosolic) enzyme with M(r) ca 65 000 and a membrane-bound enzyme with M(r) ca 165 000. Both the cytosolic and membrane bound enzyme are present in green or etiolated leaves while roots contain only the membrane enzyme. Many properties of these two enzymes are very similar to those of the cytosolic UDPGlc:nuatigenin glucosyltransferase and membrane bound UDPGlc:sterol glucosyltransferase, which were detected previously in leaves of oat seedlings. The present results strongly suggest that the ability to glucosylate the pregnane or androstane derivatives by enzyme preparations from oat seedlings may be due to relatively low substrate specificity of both UDPGlc:nuatigenin and UDPGlc:sterol glucosyltransferase.