An aminopeptidase was purified from buckwheat seed by using affinity chromatography, ionexchange chromatography and chromatofocusing. The enzyme had a molecular weight of 37, 000 as determined by gel filtration. The aminopeptidase activity, determined with L-leucine-p-nitroanilide (Leu-PNA) as the substrate, exhibited a pH optimum of 7.2. The Km value for Leu-PNAwas 140 μM. The preferred substrates were L-leucine-β-naphtylamide and Leu-pNA, although there was also high activity against L-leucyl-L-alanine and L-leucinamide. Thiol antagonists were found to be potent inhibitors against the enzyme. The enzymeexhibited less or no sensitivity to the endogeneous proteinase inhibitors, benzamidine and TPCK.

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