Transient kinetics of the reaction catalysed by magnesium protoporphyrin IX methyltransferase

The Biochemical Journal
Mark Shepherd, C N Hunter

Abstract

Magnesium protoporphyrin IX methyltransferase (ChlM), an enzyme in the chlorophyll biosynthetic pathway, catalyses the transfer of a methyl group to magnesium protoporphyrin IX (MgP) to form magnesium protoporphyrin IX monomethyl ester (MgPME). S-Adenosyl-L-methionine is the other substrate, from which a methyl group is transferred to the propionate group on ring C of the porphyrin macrocycle. Stopped-flow techniques were used to characterize the binding of porphyrin substrate to ChlM from Synechocystis PCC6803 by monitoring tryptophan fluorescence quenching on a millisecond timescale. We concluded that a rapid binding step is preceded by a slower isomerization of the enzyme. Quenched-flow techniques have been employed to characterize subsequent partial reactions in the catalytic mechanism. A lag phase has been identified that has been attributed to the formation of an intermediate. Our results provide a greater understanding of this catalytic process which controls the relative concentrations of MgP and MgPME, both of which are implicated in signalling between the plastid and nucleus in plants.

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Citations

Mar 21, 2007·Photosynthesis Research·David W Bollivar
Apr 27, 2010·Phytochemistry·Anne Stenbaek, Poul Erik Jensen
Aug 28, 2007·The Journal of Chemical Physics·Takashi IkedaKiyoyuki Terakura
Feb 13, 2016·Chemphyschem : a European Journal of Chemical Physics and Physical Chemistry·Gül Bekçioğlu-NeffDaniel Sebastiani
Oct 11, 2008·Photochemical & Photobiological Sciences : Official Journal of the European Photochemistry Association and the European Society for Photobiology·Tatsuru Masuda, Yuichi Fujita
Sep 1, 2005·The FEBS Journal·Mark ShepherdC Neil Hunter
Apr 4, 2020·The Journal of Biological Chemistry·Donald A BryantMartin J Warren

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