81(P05) 好熱性細菌、Bacillus stearothermophilusのファルネシル二リン酸合成酵素の基質特異性と阻害効果(ポスター発表の部)

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Farnesyl diphosphate (FPP) synthase[2.5.1.10] catalyzes the condensation of isopentenyl diphosphate (IPP) with dimethylallyl diphosphate(DMAPP) and with geranyl diphophate (GPP) to produce E,E-FPP. The substrate specificities of the enzyme from Bacillus stearothermophilus have been studied using the substrate analogs, which have substituents with various side chain length at 4-position of DMAPP. These results showed that the substrate specificity of the bacterial enzyme is a little different from that of the mammalian enzyme. The reactivities of allylic substrates with IPP analog 3, which has no methyl group at 3-position of IPP have been studied. This analog was accepted as homoallylic substrate to give 3-desmethyl GPP analog 4 and 3-desmethyl FPP analog 5, respectively. In the case of the chicken liver enzyme, the analog 3 hardly reacts with the allylic substrates to give noproduct. The inhibitory effects of some analogs also have been examined. The analog 6 did not react with IPP and showed noncompetetive inhibition in the respect to GPP (Fig. 1). This effect was eliminated by the addition of the detergent (Triton-X 100). The analog 4 showed no reactivity with IPP and competetive inhibition in the respect to GPP (Fig. 2). In addition, this effect was not eliminated by the addition of the detergent. On the other hand, the analog 7 which has no methyl groups at 3 and 7-positions and dihydro moiety at 6,7-position of GPP showed no reactivity and no inhibition. These findings suggest that 3-methyl group and the isopentenyl moiety of GPP is essential for the substrate recognition of the enzyme. It has been reported that the DMAPP analogs which have the various side chain reacted with IPP depending on its chain length. On the other hand, any analog having oxygen atom in its side chain showed no reactivity. Kinetic parameters, K_m and V_<max>, of the analog for the enzyme were examined. These values revealed that the analogs having oxygen atom have larger K_m values and smaller V_<max> values than those of the analogs having no oxygen atom as shown in Table 1. Interestingly, the analog 12, which has a large hydrophobic moiety in its side chain, has smaller K_m value, and showed far less reactivity with IPP.
天然有機化合物討論会の論文
1997-07-20

81(P05) 好熱性細菌、Bacillus stearothermophilusのファルネシル二リン酸合成酵素の基質特異性と阻害効果(ポスター発表の部)

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