Abstract
This chapter discusses membrane-bound thiamine triphosphatase. Thiamine triphosphate (ThTP) is present in significant quantities in most organisms, although its specific role in the cellular economy is unknown. Involvement of this compound in the function of excitable membranes has been postulated, but this hypothesis as yet remains unproved. The membrane thiamine triphosphatase described in the chapter has been first characterized in rat brain. It catalyzes the hydrolysis of the γ phosphate from ThTP, producing as products ThDP and Pi. A distinct soluble ThTPase is also described in the chapter. Enzyme activity is determined by monitoring the quantity of inorganic phosphate released from ThTP during a test interval under conditions in which the subsequent hydrolysis of ThDP can be shown to be negligible. Inorganic phosphate may be determined by any of several colorimetric assays. The chapter describes the source of the enzyme thiamine triphosphatse. Detectable levels of the enzyme have been demonstrated in crude membrane preparations of most soft tissues of the rat, highest specific activities being found in the intestine and kidney.