Abstract
The properties of soluble and microsomal thiamine triphosphatase (TTPase) in rat brain were examined. The subcellular distributions and the pH optima of these enzyme activities differ markedly. TTPase seems to be distinct from a general nucleoside triphosphatase. The TTPase activities have an absolute divalent cation requirement which is fulfilled by Mg++ or Ca++ in microsomes and by Mg++, but not Ca++, in the soluble fraction. Addition of a physiological concentration of Ca++ markedly inhibited the soluble TTPase activity.
