Potassium-stimulating mechanism of geranylgeranyl diphosphate synthase of Methanobacterium thermoformicicum SF-4.
The catalytic properties of geranylgeranyl diphosphate (GGPP) synthase [EC 2.5.1.29] purified from Methanobacterium thermoformicicum SF-4 were studied by kinetic procedures. The plots of 1/v versus 1/[S] and inhibition patterns by enzyme reaction products, PPi and GGPP, showed that the GGPP synthase reaction mechanism is an ordered-sequential Bi Bi one. Monovalent cations at low concentration (0.05 M) enhanced the enzyme activity, but at high concentration (0.4 M) they were inhibitory, except for K+. The K+ ion was found to be a modifier forming a parallel reaction pathway and accelerated the binding of substrates to the enzyme, especially the binding of isopentenyl diphosphate (IPP). When substrate concentrations are near the Km values, the rate-limiting step of the GGPP synthase reaction may be the substrate-binding step, probably the IPP-binding step, rather than the conversion step of the enzyme-farnesyl diphosphate-IPP complex to the enzyme-PPi-GGPP complex.
Tachibana
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A
Department of Biology, Faculty of Science, Osaka City University.
Tanaka
T
T
Taniguchi
M
M
Oi
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S
D019883:Alkyl and Aryl Transferases; D002414:Cations, Monovalent / Q000494:pharmacology; D051231:Farnesyltranstransferase; D007700:Kinetics; D017014:Methanobacterium / Q000201:enzymology*; D011188:Potassium / Q000494:pharmacology*; D014166:Transferases / Q000037:antagonists & inhibitors / Q000187:drug effects*
D002414:Cations, Monovalent; D014166:Transferases; D019883:Alkyl and Aryl Transferases; D051231:Farnesyltranstransferase; D011188:Potassium