Kinetic properties of Rhodanese from African locust bean seeds (Parkia biglobosa)

Abstract

African locust bean (Parkia biglobosa) is a legume which can be processed into condiment. Rhodanese is a sulphurtransferase enzyme. It catalyses the degradation of cyanide to a less toxic metabolite, thiocyanate. Rhodanese purication and biochemical characterization were carried out in this study. The activity of this enzyme from Parkia biglobosa was evaluated and the kinetics of the rhodanese enzyme reaction, including pH and temperature profiles, substrate specificity and effects of metal ions were assessed. Studies on the rhodanese enzyme from other systems have been compared with the results of this study. Rhodanese was isolated from Parkia biglobosa and purified using ammonium sulphate precipitation, CM-Sephadex, and Reactive Blue 2-agarose column chromatography. The purified enzyme has a specific activity of 3.69 RU/mg with a percent yield of 0.20. Km and Vmax values of 7.61 mM and 0.65 RU/ml/min were obtained respectively when KCN was used as a substrate while values of 11.59 mM and 0.57 RU/ml/min was obtained with Na2S2O3. The enzyme showed preference for sodium thiosulphate (Na2S2O3) among different substrates tested namely Mercapto-ethanol (HOCH2CH2SH), Ammonium per sulphate (NH4)2S2O8), Ammonium sulphate (NH4)2SO4), Sodium sulphate (Na2SO4), Sodium metabisulphite (Na2SO5). Optimum temperature and pH of 50?C and 8 were obtained respectively. Chloride salts tested showed little or no inhibitory effect at 1 mM concentration with the exception of HgCl2 and MnCl2. However at 10 mM concentration, the divalent metals; MnCl2 HgCl2, CaCl2, BaCl2 inhibited the enzyme. The present study showed that locust bean seeds possess a cyanide detoxifying enzyme with suitable kinetic properties which renders it safe for consumption.