title: Competitive inhibitions of the chlorophyll synthase of Synechocystis sp. strain PCC 6803 by bacteriochlorophyllide a and the bacteriochlorophyll synthase of Rhodobacter sphaeroides by chlorophyllide a.
abstract: The photosynthetic growth of Synechocystis sp. strain PCC 6803 is hampered by exogenously added bacteriochlorophyllide a (Bchlide a) in a dose-dependent manner. The growth inhibition caused by Bchlide a, however, is relieved by an increased level of exogenously added chlorophyllide a (Chlide a). The results are explained by the competitive inhibition of chlorophyll synthase by Bchlide a, with inhibition constants (K(I)s) of 0.3 mM and 1.14 mM in the presence of sufficient geranylgeranyl pyrophosphate (GGPP) and phytyl pyrophosphate (PPP), respectively. Surprisingly, the bacteriochlorophyll synthase of Rhodobacter sphaeroides is inhibited competitively by Chlide a, with K(I)s of 0.54 mM and 0.77 mM in the presence of sufficient GGPP and PPP, respectively. Consistently, exogenously added Chlide a inhibits the metabolic conversion of exogenously added Bchlide a to bacteriochlorophyll a by an R. sphaeroides bchFNB-bchZ mutant that neither synthesizes nor metabolizes Chlide a. The metabolic inhibition by Chlide a, however, is relieved by the elevated level of Bchlide a. Thus, the chlorophyll synthase of Synechocystis sp. PCC 6803 and the bacteriochlorophyll synthase of R. sphaeroides, both of which perform ping-pong-type reactions, are inhibited by Bchlide a and Chlide a, respectively. Although neither inhibitor is catalyzed by the target enzyme, inhibitions in the competitive mode suggest a structural similarity between their active sites.
authors.affiliation: Department of Life Science and Basic Science Institute for Cell Damage Control, Sogang University, Seoul 121-742, South Korea.
authors.forename: Eui-Jin
authors.initials: EJ
authors.lastname: Kim
authors.forename: Jeong K
authors.initials: JK
authors.lastname: Lee
mesh_terms: D001426:Bacterial Proteins / Q000378:metabolism; D025541:Bacteriochlorophyll A / Q000378:metabolism; D019729:Carbon-Oxygen Ligases / Q000378:metabolism*; D002735:Chlorophyllides / Q000378:metabolism / Q000494:pharmacology*; D002851:Chromatography, High Pressure Liquid; D004790:Enzyme Induction / Q000187:drug effects; D004791:Enzyme Inhibitors / Q000494:pharmacology; D008954:Models, Biological; D010957:Plasmids; D012242:Rhodobacter sphaeroides / Q000187:drug effects* / Q000201:enzymology* / Q000254:growth & development; D046939:Synechocystis / Q000187:drug effects* / Q000201:enzymology* / Q000254:growth & development
chemical_list: D001426:Bacterial Proteins; D025541:Bacteriochlorophyll A; D002735:Chlorophyllides; D004791:Enzyme Inhibitors; C034388:chlorophyllide a; D019729:Carbon-Oxygen Ligases; C105512:bacteriochlorophyll a synthase; C026901:chlorophyll synthetase