Purification and kinetic characterization of the magnesium protoporphyrin IX methyltransferase from Synechocystis PCC6803

Shepherd, Mark and Reid, James D. and Hunter, C. Neil (2003) Purification and kinetic characterization of the magnesium protoporphyrin IX methyltransferase from Synechocystis PCC6803. Biochemical Journal, 371 (Pt 2). pp. 351-60. ISSN 0264-6021. (The full text of this publication is not available from this repository)

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Official URL
http://dx.doi.org/10.1042/BJ20021394

Abstract

Magnesium protoporphyrin IX methyltransferase (ChlM), catalyses the methylation of magnesium protoporphyrin IX (MgP) at the C(6) propionate side chain to form magnesium protoporphyrin IX monomethylester (MgPME). Threading methods biased by sequence similarity and predicted secondary structure have been used to assign this enzyme to a particular class of S-adenosyl-L-methionine (SAM)-binding proteins. These searches suggest that ChlM contains a seven-stranded beta-sheet, common among small-molecule methyltransferases. Steady-state kinetic assays were performed using magnesium deuteroporphyrin IX (MgD), a more water-soluble substrate analogue of MgP. Initial rate studies showed that the reaction proceeds via a ternary complex. Product (S-adenosyl-L-homocysteine; SAH) inhibition was used to investigate the kinetic mechanism further. SAH was shown to exhibit competitive inhibition with respect to SAM, and mixed inhibition with respect to MgD. This is indicative of a random binding mechanism, whereby SAH may bind productively to either free enzyme or a ChlM-MgD complex. Our results provide an overview of the steady-state kinetics for this enzyme, which are significant given the role of MgP and MgPME in plastid-to-nucleus signalling and their likely critical role in the regulation of this biosynthetic pathway.

Item Type: Article
Subjects: Q Science
Divisions: Faculties > Science Technology and Medical Studies > School of Biosciences
Depositing User: Mark Shepherd
Date Deposited: 01 Sep 2011 16:12
Last Modified: 15 Apr 2014 07:51
Resource URI: http://kar.kent.ac.uk/id/eprint/28077 (The current URI for this page, for reference purposes)
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