Substrate specificities of medium-prenylchain elongating enzymes, hexaprenyl- and heptaprenyl diphosphate synthases

In order to investigate substrate specificities of medium-prenylchain elongating enzymes, hexaprenyl diphosphate (HexPP) synthase from Micrococcus luteus B-P 26 and heptaprenyl diphosphate (HepPP) synthase from Bacillus subtilis, we examined the reactivities of 3-alkyl group homologs of allylic or homoallylic substrates for these enzymes. Only one molecule of but-3-enyl diphosphate (2b), which lacks a methyl group at the 3-position of isopentenyl diphosphate (2a) condensed with farnesyl diphosphate (1, FPP) to give E-norgeranylgeranyl diphosphate in the reaction catalyzed by either enzyme. lbut-3-enyl diphosphate (2c) reacted as a homoallylic substrate with FPP to give a mixture of (all-E)-3-ethyl-7,11,15-trimethylhexadeca-2,6,10,14-tetraenyl- and (all-E)-3,7-diethyl-11,15,19-trimethyleicosa-2,6,10,14,18-pentaenyl diphosphates by the condensation with one or two molecules of (2c), respectively, by the reaction of HexPP synthase. 3-Propylbut-3-enyl diphosphate (2d) also reacted with FPP to give a mixture of the corresponding single and double condensation products, respectively, by the action of the same synthase. other hand, HepPP synthase reaction of (2c) or (2d) with FPP gave (all-E)-3-ethyl-7,11,15-trimethylhexadeca-2,6,10,14-tetraenyl diphosphate or (all-E)-3-propyl-7,11,15-trimethylhexadeca-2,6,10,14-tetraenyl diphosphate as a single product, respectively. r, 3-butylbut-3-enyl diphosphate (2e), norfarnesyl diphosphate (1a) and norgeranylgeranyl diphosphate (1b) were never accepted as substrates by either of the enzymes at all.