Metabolism of Sinapine in Mustard Plants. II. Purification & Some Properties of Sinapine Esterase

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Abstract
An enzyme that catalyzes the hydrolysis of sinapine into sinapic acid and choline has been purified 20-fold from white mustard seedlings (Brassica hirta) seedlings. The esterase also hydrolyzes acetylcholine. The pH optimum is 10 for sinapine and 8 for acetylcholine. A number of metal activators were studied but none were found to increase the enzymatic rate of hydrolysis. Choline, iodoacetate and p-chloromercuribenzoate were found to inhibit the reaction. The enzyme was markedly activated by such sulfhydryl group reagents as cysteine and glutathione. Eserine did not inhibit at low concentrations, thus the enzyme cannot be considered as a true choline esterase by the usual definition. On the basis of these and other properties sinapine esterase cannot be identified with any other esterase described in the literature.