Making light work of enzyme catalysis: protochlorophyllide oxidoreductase

Conserved Chloroplast Open-reading Frame ycf54 Is Required for Activity of the Magnesium Protoporphyrin Monomethylester Oxidative Cyclase in Synechocystis PCC 6803

“…Early studies of the cyclase employed enzyme assays based on fractionated extracts prepared from chloroplasts and could not benefit from current methods using the recombinant production of proteins. The lack of any mechanistic data on the MgPME cyclase is in sharp contrast to recent progress in the kinetic analysis of other enzymes in the Chl biosynthetic pathway, for example with Mg chelatase, MgP methyltransferase, and PChlide oxidoreductase (35)(36)(37). The identification of Ycf54 as a factor critical for the activity of MgPME cyclase in vivo should allow further progress with the biochemical analysis of this step in chlorophyll biosynthesis.…”

The First Catalytic Step of the Light-driven Enzyme Protochlorophyllide Oxidoreductase Proceeds via a Charge Transfer Complex

“…C-17-C-18 double bond of the D-ring of protochlorophyllide (Pchlide) to produce chlorophyllide (Chlide), a key regulatory step in the chlorophyll biosynthetic pathway (1). POR is a member of the "RED" superfamily of enzymes (reductases, epimerases, dehydrogenases) (2, 3), which catalyze NADP(H)-or NAD(H)-dependent reactions involving hydride and proton transfers (4).…”

Broadened Substrate Specificity of 3-Hydroxyethyl Bacteriochlorophyllide a Dehydrogenase (BchC) Indicates a New Route for the Biosynthesis of Bacteriochlorophyll a

“…Chelator Treatment of BchC-Samples of purified BchC were preincubated in the presence of up to 100 mM EDTA or EGTA (75 min at 48°C). Subsequently, coupled BchC activity experiments and assays in the presence of substrate 3 1 -OH-BPheide a 3 (1) or Zn-3 1 -13 2 -di-OH-Pheide a 3 (5) did not reveal reduced BchC activities when compared with the respective control experiment (not shown). These results did not reflect the outcome of related experiments for well characterized zinc-dependent MDR enzymes: chelation of the zinc ions of yeast alcohol dehydrogenase (53) and L-threonine dehydrogenases from Pyrococcus furiosus and Thermococcus kodakaraensis (54,55) resulted in enzymatic inactivation.…”

“…Then the reduction of the peripheral vinyl group at C8 results in the formation of protochlorophyllide a (Pchlide; compound 11; see Subsequently, reduction of the C17/C18 double bond of ring D leads to the formation of the chlorin ring structure of chlorophyllide a (Chlide; compound 12). Two unrelated enzymes have developed for the regio-and stereospecific reduction of the fully conjugated Pchlide ring system: light-dependent protochlorophyllide oxidoreductase performs a light-driven, NADPH-dependent reduction, whereas the ATP-dependent multisubunit enzyme dark-operative protochlorophyllide a oxidoreductase (DPOR) uses nitrogenase-like biochemistry (3)(4)(5)(6).…”