Journal
BIOCHEMICAL JOURNAL
Volume 382, Issue -, Pages 1009-1013Publisher
PORTLAND PRESS
DOI: 10.1042/BJ20040661
Keywords
chlorophyll biosynthesis; magnesium protoporphyrin IX methyltransferase; methylation; porphyrin
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Magnesium protoporphyrin IX methyltransferase (Ch1M), 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 Ch1M 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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