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.The biosynthetic pathways for bacteriochlorophyll a (Bchl a) and chlorophyll a (Chl a) share the metabolic steps from protoporphyrin IX to chlorophyllide a (Chlide a) (Fig.

Elucidation of Genetic Backgrounds Necessary for Chlorophyll a Biosynthesis Toward Artificial Creation of Oxygenic Photosynthesis

“…Purple sulfur/non-sulfur bacteria produce only BChl a, and indeed have the bchG gene. This indicates that BchG does not react with chlorophyllide a but is specific to bacteriochlorophyllide a, as shown in the previous report (Kim and Lee 2010). Thus, in order to enable purple bacteria produce Chl a, we probably have to incorporate the chlG gene into them.…”

Peroxidase and Photoprotective Activities of Magnesium Protoporphyrin IX

“…In this work, several Bch biosynthetic mutants of R. sphaeroides were cultured under anaerobic conditions in the presence of DMSO, and the Bch intermediates that accumulated in cells or culture supernatants were solvent-extracted and examined for antioxidative activity. The bch mutants used were as follows: bchM mutant, bchFNB mutant [20], bchZ mutant [18,20], bchF mutant [18][19][20], bchZF mutant [18], bchC mutant [20], and bchG mutant [20] (Fig. 1A).…”

“…Intermediates of the Bch biosynthetic pathway were purified using bchM mutant, bchFNB mutant [20], bchZ mutant [18,20], bchF mutant [18][19][20], bchZF mutant [18], bchC mutant [20], and bchG mutant [20]. The mutants were cultivated in Sis medium supplemented with Tween 80 (0.03%) under dark anaerobic conditions (with DMSO).…”

Incomplete Hydrogenation by Geranylgeranyl Reductase from a Proteobacterial Phototroph Halorhodospira halochloris, Resulting in the Production of Bacteriochlorophyll with a Tetrahydrogeranylgeranyl Tail

“…Although Chl and BChl species possess specific core π-skeletons and peripheral substituents, the penultimate and last biosynthetic steps for all the photosynthetic (B)Chl pigments except Chl c are common, where the order of the two steps can be switched. The esterification of geranylgeranyl diphosphate into the substituent at the carbon 17 (C17) position of (bacterio)chlorophyllide ( 10 – 12 ) is the penultimate step. The esterification is catalyzed by an enzyme designated as (B)Chl synthase encoded by the bchG/chlG gene.…”