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, containi ng a planar ring system (5 alpha-H or Delta(5)), e.g. pregnenolone, ep iandrosterone 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 reac tions: 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 bo und enzyme are present in green or etiolated leaves while roots contai n only the membrane enzyme. Many properties of these two enzymes are v ery similar to those of the cytosolic UDPGlc:nuatigenin glucosyltransf erase and membrane bound UDPGlc:sterol glucosyltransferase, which were detected previously in leaves of oat seedlings. The present results s trongly suggest that the ability to glucosylate the pregnane or andros tane derivatives by enzyme preparations from oat seedlings may be due to relatively low substrate specificity of both UDPGlc:nuatigenin and UDPGlc:sterol glucosyltransferase.