Abstract

The thiaminase enzymes were partially purified and characterized from Tilapia zillii fillet (flesh) and liver using ammonium sulphate precipitation. The enzyme showed specific activities of 5.20 and 1.17 umol/min/mg of protein respectively for T. zillii fillet and liver. The enzymes exhibited a maximal activity at pH 5.0 and 7.0 for the liver and fillet, respectively. The Michealis constant for thiamine as substrate for both tissues was of 0.4 mM but 0.5 mM and 22 mM were obtained for aniline as substrate in the liver and fillet respectively. The optimum temperature of T. zillii thiaminases were 50 and 85°C for fillet and liver, respectively. Amino acids of fillet did not show significant effect on the enzyme activity but in the liver, the amino acids showed great inhibition with lysine showing complete inhibition of the enzyme. The thiaminase activities of fillet and liver were inhibited by divalent metal ions (Zn²⁺, Sn²⁺, Mg²⁺ and Hg²⁺) but the enzyme from the liver was completely inhibited by Mg²⁺. The inhibitors (2-Mercaptoethanol, ethylenediaminetetraacetic acid (EDTA), reduced glutathione (GSH), citrate and ascorbic acid) also showed different inhibitory effects on the enzymes from both tissues. EDTA and ascorbic acid did not inhibit the fillet thiaminase enzyme.

Key words: Tilapia zillii, liver, fillet, thiaminase, characterization, kinetic properties.