Deuterium exchange studies and kinetics of Isopentenyldiphosphate Isomerase (IDI)
Jonnalagadda, Venkatadurga B.
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Isopentenyldiphosphate Isomerase (IDI) is a key enzyme in isoprenoid biosynthesis catalyzing the conversion of homoallylic isopentenyl pyrophosphate (IPP) to a more electrophilic dimethylallyl pyrophosphate (DMAP). The significance of this enzyme arises from the wide variety of roles isoprenoid compounds carry out ranging from cell wall and glycoprotein biosynthesis, electron transport, signal transduction, hormonal and respiratory functions in eukaryotes just to name a few. This makes IDI an essential enzyme in plants, archaea, eukaryotes and some bacteria that depend on mevalonate pathway for isoprenoid biosynthesis. The significance of this enzyme both from a mechanistic perspective and also as a potential drug target makes it an intriguing target to study. Deuterium exchange into the reaction catalyzed by IDI has been studied by carrying out the reaction in D 2 O and relative rates of the formation of different products have been established. Following the incorporation of deuterium into substrate IPP has revealed interesting aspects about the number of turnovers a substrate undergoes in the active site once bound to the enzyme. It was also observed that E. coli IDI is more stereospecific at C2 carbon during isomerization compared to its yeast counterpart. The activity of IDI in imidazole buffer (in H 2 O) has been measured using 1 H NMR ( k cat = 0.08 s -1 ). Overall, this study has revealed some important insights into the kinetics of different processes that occur at the active site of IDI during the isomerization of IPP.