title: Kinetic basis for linking the first two enzymes of chlorophyll biosynthesis.
abstract: Purified recombinant proteins from Synechocystis PCC6803 were used to show that the magnesium chelatase ChlH subunit stimulates magnesium protoporphyrin methyltransferase (ChlM) activity. Steady-state kinetics demonstrate that ChlH does not significantly alter the K(m) for the tetrapyrrole substrate. However, quenched-flow analysis reveals that ChlH dramatically accelerates the formation and breakdown of an intermediate in the catalytic cycle of ChlM. In light of the profound effect that ChlH has on the methyltransferase catalytic intermediate, the pre steady-state analysis in the current study suggests that ChlH is directly involved in the reaction chemistry. The kinetic coupling between the chelatase and methyltransferase has important implications for regulation of chlorophyll biosynthesis and for the availability of magnesium protoporphyrin for plastid-to-nucleus signalling.
authors.affiliation: Robert Hill Institute for Photosynthesis and Krebs Institute for Biomolecular Research, Department of Molecular Biology and Biotechnology, University of Sheffield, UK. shepherd@secsg.uga.edu
authors.forename: Mark
authors.initials: M
authors.lastname: Shepherd
authors.forename: Samantha
authors.initials: S
authors.lastname: McLean
authors.forename: C Neil
authors.initials: CN
authors.lastname: Hunter
mesh_terms: D002734:Chlorophyll / Q000096:biosynthesis*; D005798:Genes, Bacterial; D007700:Kinetics; D008190:Lyases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D008780:Methyltransferases / Q000235:genetics / Q000378:metabolism*; D008954:Models, Biological; D021122:Protein Subunits; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D046939:Synechocystis / Q000235:genetics / Q000378:metabolism*
chemical_list: D021122:Protein Subunits; D011994:Recombinant Proteins; D002734:Chlorophyll; D008780:Methyltransferases; C060234:magnesium-protoporphyrin methyltransferase; D008190:Lyases; C086788:magnesium chelatase