Compounds containing reduced forms of phosphorus (i.e. P(III) or P(I)) are widespread in Nature. Despite this, few studies have been reported detailing investigations of enzymes that catalyze phosphorus redox chemistry. In this program, we are interested in the mechanisms of catalysis of two such proteins, phosphite dehydrogenase (PtxD) and hypophosphite dioxygenase (HtxA). These enzymes perform entirely unprecedented reactions and will be studied to gain a better understanding of their catalytic mechanisms as well as their evolutionary origin. In addition, we have shown that phosphite dehydrogenase is a versatile cofactor regeneration enzyme, and a better understanding of catalysis may allow improvements in catalytic efficiency. The studies in this grant focus on the associative vs. dissociative character of the oxidation of phosphite to phosphate by PtxD. To this end, investigations with alternative substrates and site directed mutants will be conducted, and a major focus will be devoted to obtaining crystallographic characterization. The studies on HtxA focus on potential use of alternative substrates as well as developing a fundamental understanding of the mode of catalysis.
