Substrate Specificities of Wild and Mutated Farnesyl Diphosphate Synthases from Bacillus Stearothermophilus with Artificial Substrates

To determine the substrate specificities of wild and mutated types of farnesyl diphosphate (FPP) synthases from Bacillus stearothermophilus, we examined the reactivities of 8-hydroxygeranyl diphosphate (HOGPP) and 8-methoxygeranyl diphosphate (CH₃OGPP) as allylic substrate homologs.

The wild-type FPP synthase reaction of HOGPP (and CH₃OGPP) with isopentenyl diphosphate (IPP) gave hydroxyfarnesyl- (and methoxyfarnesyl-) diphosphates that stopped at the first stage of condensation.

On the other hand, with mutated type FPP synthase (Y81S), the former gave hydroxygeranylgeranyl diphosphate as the main double-condensation product together with hydroxyfarnesyl diphosphate as a single-condensation product and a small amount of hydroxygeranylfarnesyl diphosphate as a triple-condensation product. Moreover, the latter gave a double-condensation product, methoxygeranylgeranyl diphosphate, as the main product and only a trace of methoxyfarnesyl diphosphate was obtained.