Physicochemical and kinetic characteristics of rhodanese from the liver of African catfish Clarias gariepinus Burchell in Asejire lake Omolara Titilayo Akinsiku Æ Femi Kayode Agboola Æ Adenike Kuku Æ Adeyinka Afolayan Received: 9 December 2008 / Accepted: 21 April 2009 / Published online: 18 June 2009 Ó Springer Science+Business Media B.V. 2009 Abstract Two forms of rhodanese were purified from the liver of Clarias gariepinus Burchell, desig- nated catfish rhodanese I (cRHD I) and rhodanese II (cRHD II), by ion-exchange chromatography on a CM- Sepharose CL-6B column and gel filtration through a Sephadex G-75 column. The apparent molecular weight obtained for cRHD I and cRHD II was 34,500 ± 707 and 36,800 ± 283 Da, respectively. The subunit molecular weight determined by sodium dodecyl sulphate–polyacrylamide gel electrophoresis was 33,200 ± 283 and 35,100 ± 141 Da for cRHD I and cRHD II, respectively. Atomic absorption spec- trophotometric analysis revealed that cRHD II con- tained a high level of iron (Fe), which presumably was responsible for the brownish colour of the preparation. In contrast, no Fe was identified in cRHD I, and its preparation was colourless. Further characterization of cRHD II gave true Michaelis–Menten constant (K m ) values of 25.40 ± 1.70 and 18.60 ± 1.68 mM for KCN and Na 2 S 2 O 3 , respectively, an optimum pH of 6.5 and an optimum temperature of 40°C. The Arrhenius plot of the effects of temperature on the reaction rate consisted of two linear segments with a break occurring at 40°C. The apparent activation energy values from these slopes were 7.3 and 72.9 kcal/mol. Inhibition studies on the cRHD II enzyme showed that the activity of the enzyme was not affected by Mn 2? , Co 2? , Sn 2? , Ni 2? and NH 4 ? , but Zn 2? inhibited the enzyme considerably. Keywords Aquatic organisms Á Asejire Lake Á Catfish (Clarias gariepinus) Á Cyanide Á Cyanide detoxification Á Cyanogenic plants Á Fish Á Rhodanese Introduction Rhodanese (thiosulphate: cyanide sulphurtransferase, EC 2.8.1.1) is a sulphur transferase that catalyses, in vitro, the formation of thiocyanate from cyanide and thiosulphate or other suitable sulphur donors. Differ- ent thiosulphonates are able to replace thiosulphate in the rhodanese reaction (Sorbo 1953a), and sulphite, sulphanate and persulphide can also serve as donor substrates (Sorbo 1957; Villarejo and Westley 1963; Koj 1968; Nagahara et al. 1999). In vivo, however, the enzyme is multifunctional: it supplies sulphide for the formation of iron–sulphur centres, maintains the sulphane pool and participates in selenium metabolism and thiamine biosynthesis (Smith and Urbanska 1986; The data presented in this report is part of the research carried out by O. T. Akinsiku in partial fulfilment for the degree of Master of Science in Biochemistry at the Obafemi Awolowo University, Ile-Ife, Nigeria. O. T. Akinsiku Á F. K. Agboola (&) Á A. Kuku Á A. Afolayan Department of Biochemistry, Obafemi Awolowo University, Ile-Ife, Nigeria e-mail: fkagbo@oauife.edu.ng 123 Fish Physiol Biochem (2010) 36:573–586 DOI 10.1007/s10695-009-9328-4