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Kinetic basis for linking the first two enzymes of chlorophyll biosynthesis
Author(s) -
Shepherd Mark,
McLean Samantha,
Hunter C. Neil
Publication year - 2005
Publication title -
the febs journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.981
H-Index - 204
eISSN - 1742-4658
pISSN - 1742-464X
DOI - 10.1111/j.1742-4658.2005.04873.x
Subject(s) - biochemistry , biosynthesis , chemistry , tetrapyrrole , protoporphyrin ix , enzyme , kinetics , chloroplast , synechocystis , protein subunit , chlorophyll , biology , mutant , gene , quantum mechanics , physics , photodynamic therapy , organic chemistry
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.