TISSUE DISTRIBUTION AND BIOCHEMICAL CHARACTERIZATION OF BETA-CYANOALANINE SYNTHASE FROM COMMON BEAN SEEDS (PHASEOLUS VULGARIS)

Abstract

Cyanide is produced throughout a plant's life cycle, its production increases during certain developmental stages such as seed germination, seedling elongation, fruit ripening and senescence. Beta-cyanoalanine synthase is the most important cyanide metabolizing enzyme found in plants. This work is aimed at studying the tissue distribution, partial purification and some physicochemical properties of β-cyanoalanine synthase from bean seeds (Phaseolus vulgaris). β-cyanolalanine synthase was isolated and partially purified using a combination of ammonium sulphate precipitation, desalting on Sephadex G-10 and gel filtration chromatography on Sephacryl S-200 column. The biochemical characteristics of the enzyme were investigated. Results obtained from this work showed that β-cyanolalanine synthase is more concentrated in the seeds (20.53 nmol/HS/mg) when compared 2 to the cotyledons (10.08 nmol/HS/mg) and the seed coats (5.82 nmol/HS/mg). The partially purified 2 2 enzyme showed a specific activity of 26.77 nmol/HS/mg and an apparent molecular weight of about 2 60,000Da, K values for cyanide and L-cysteine of 0.741 mM and 1.724 mM respectively. The V max m value obtained for cyanide was 25.00 nmol/H S/ml/minwhile that of L-cysteine was 2 o666.67nmol/H S/ml/min. The enzyme showed an optimum temperature of 40C and optimum pH of 2 10.0.Studies on the effect of chloride salt indicated that NaCl and MnCl had strong inhibitory effect 2 on the enzyme; NHCl had slight negative effect while KCl and ZnCl activated the enzyme dose 4 2 dependently.This study showed the presence of β-cyanoalanine synthase in bean seeds which is believed to function in the detoxification of cyanide produced in its tissues especially during germination.