Enzymatic synthesis of quinolizidine alkaloid esters: a tigloyl-CoA: 13-hydroxylupanine O-tigloyltransferase from Lupinus albus L.

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Abstract
A tigloyl-CoA: 13-hydroxylupanine O-tigloyl-transferase could be demonstrated in crude enzyme preparations from Lupinus albus seedlings. The enzyme activity increases concomitantly with for formation of 13-tigloyloxylupanine in developing lupin seedlings. The transferase catalyzes specifically the transfer of an acyl group to 13-hydroxylupanine. The apparent Km-values are 140 μM for tigloyl-CoA and 18 μM for 13-hydroxylupanine. Other hydroxylated compounds, e.g., lupinine, 4-hydroxylupanine, and cholesterol are not acylated. The transferase shows optimal activity at pH 7–8 and at 30°C. It is activated by dithioerythritol and inhibited by thiol reagents. Tigloyl-CoA can be replaced as acyl donor by benzoyl-CoA and to a lesser extent by valeroyl-CoA, 3-methylbutyryl-CoA, butyryl CoA and propionyl-CoA but not acetyl-CoA. Preliminary evidence indicates that the transfer of the tigloyl and benzoyl moieties is catalyzed by different enzymes. The transferase activity could only be demonstrated in plants which produce quinolizidine alkaloids.