I. K. Kolas, A. F. Makarchikov

Grodno State Agrarian University,
Institute of Biochemistry of Biologically Active Compounds,
National Academy of Sciences of Belarus;
e-mail: a_makarchikov@yahoo.com

The enzymes involved in thiamine triphosphate (ThTP) metabolism in birds are not characteri­zed so far. The aim of the present work was to study some properties of ThTPase in chicken liver. In liver homogenate, ThTPase activity has been found to display a bell-like pH-profile with a maximum of 5.5-6.0. Low activity was observed without divalent metal ions, while the addition of Mg²⁺ or Ca²⁺, each at 5 mM concentration, enhanced the rate of ThTP hydrolysis by a factor of 17-20. In the presence of 5 mM Mg²⁺ an apparent K_m of the enzyme for ThTP was estimated by the method of non-linear regression as well as from the Hanes plot to be 1.7-2.2 mM. Monovalent anions such as I^–, SCN^–, NO₃^–, Br^–, Cl^– (at 150 mM concentration) showed inhibitory effect decreasing the rate of ThTPase reaction by 20-60%. After the homogenate was centrifuged, more than 85% of ThTPase activity was revealed in the fraction of insoluble particles indicating a membrane localization of the enzyme. The precipitate treatment with 1% sodium deoxycholate caused about 53% solubilization of the activity. During Toyopeal HW-55 chromatography, ThTPase activity was eluted simultaneously with ATPase and ITPase peaks in the void volume of the column. Thus, a non-specific high molecular mass protein complex seems to be involved in ThTP hydrolysis in the chicken liver. The chicken liver phosphatase is clearly distinguishable from all membrane-bound ThTPases reported previously.