THIAMINE INTESTINAL TRANSPORT AND PHOSPHORYLATION - A STUDY INVITRO OF POTENTIAL INHIBITORS OF SMALL INTESTINAL THIAMINE-PYROPHOSPHOKINASE USING A CRUDE ENZYMATIC PREPARATION

Using as enzymatic source the cytoplasmatic fraction of enterocytes isolated from the rat small intestine, thiamine-pyrophosphokinase activity was studied with a radiometric method using [thiazole-2-14C] thiamine. The Km value for thiamine was 2.14 × 10-6 and V 0.87 nmol of thiamine pyrophosphate mg-1 protein h-1. Eleven thiamine structural analogs and derivatives were assayed for their inhibitory action on the small intestine thiamine-pyrophosphokinase activity. Their K1 values were: pyrithiamine, 2.25 × 10-6M; thiamine mono- phosphate, 4 × 10-6 M; 2'-ethylthiamine, 8 × 10-6 M; 2'-butylthiamine, 6 × 10'6; chloroethylthiamine and dimethalium, 1.5 × 10-6M; am-prolium, 1.8 × 10-4M; L-582571, 1.65 × 10-4; oxythiamine, 4.2 × 10-3 M. Of the miscellaneous compounds tested (toxopyrimidine, Na-pyrophosphate, choline, L-phenylalanine, ethyl-urethane and 5-fluorouracil), none had any inhibitory action on intestinal thiamine-pyrophosphokinase activity, even if used at concentrations hundred times higher than that of labelled thiamine. © 1979 Informa UK Ltd All rights reserved: reproduction in whole or part not permitted.