Characterization of Thiosulphate: Cyanide sulphur transferase from the gut and body segments of Earthworm (Hyperiodrilus africanus)

Abstract

Cyanide compounds that are by products of industrial activities are known to pose serious environmental pollution. The use of these cyanide compounds by the mining industry, along with limitations in the analysis and monitoring of these compounds, raises serious concerns regarding environmental protection and public safety. Hyperiodrilus africanus (earthworm) is directly employed within bioremediation strategies to promote biodegradation of organic contaminants and thus could be employed to rejuvenate cyanide contaminated soils. Cyanides detoxification could also prevent the risk of cyanide poisoning in poultry animals by converting cyanides in forages to a less toxic compound. This work is designed to extract and characterize rhodanese (thiosulphate: cyanide sulphur transferase, (EC 2.8.1.1) from the gut and body segments of H. africanus collected from the swampy area along Uren bank river in Ikenne community of Ogun State, Nigeria. Our results show total rhodanese activities of 1434.50 RU and 2274.28 RU and specific activities of 108.01 RUmg^-1 and 83.1901 RUmg^-1 in the gut and body segments of H. africanus respectively. The optimum temperature of 25 °C and optimum pH of 10.5 were obtained for both the gut and body segments enzymes. The enzyme obeyed Michaelis-Menten kinetics and the kinetic constants, K_m and V_max in the gut segment were 33.33 mM and 62.50 RU/ml for KCN substrate and 22.22 mM and 41.67 RU/ml for Na₂S₂O₃ substrates. In the body segment, the K_m and V_max were 33.33 mM and 83.33 RU/ml; 15.38 mM and 4.00 RU/ml for the KCN and Na₂S₂O₃ substrates respectively. Hence, we conclude that the enzyme is more specific for  Na₂S₂O₃ than KCN as substrates, though maximum activity was observed in the body segment for KCN substrate. Ca²⁺, Mg²⁺, Ba²⁺, K⁺, Na⁺, Cu²⁺ and Zn²⁺ metal ion salts activated the body segment rhodanese at 1 mM and 5 mM concentrations while they have no effect on the gut segment rhodanese from earthworm. On the basis of these findings we conclude that earthworm could detoxify cyanide-containing wastes/forages and therefore promote biodegradation.

Keywords: Rhodanese, earthworm, environmental protection, cyanide detoxification, bioremediation