[Interaction of thiamine diphosphate with magnesium ion]

The action of magnesium ion on the exchange rate of the proton in C2 of thiamine and thiamine diphosphate is studied at different values of pD. Above pD 5 the ion Mg2+ increases this exchange rate. The phenomenon is markedly enhanced for TDP rather than thiamine and increases with pD. Below pD 5 magnesium decreases the exchange rate. This decrease is greater for TDP than for thiamine. The maximum effect is reached at a magnesium concentration of 0.5/1 for thiamine and of 1/1 for TDP. T1 measurements are made for different pH values with and without magnesium ion. Results seem to prove that an increase in pD values from 3.9 to 5.9 leads to an accentuation of the molecules "folded" form. Nevertheless for a given pD value the TDP-Mg complex seems to have a more "folded" form than TDP.