One of the final reactions of chlorophyll (Chl) biosynthesis, e.g: photoreduction of protochlorophyllide (Pchlid) to chlorophyllide (Chlid) is a light-induced process in Angiosperm plants and it is catalyzed by light-dependent NADPH-Pchlid oxidoreductase (22.214.171.124; LPOR). In darkness, Chl biosynthesis is stopped at the stage of Pchlid formation. Seedlings and plastids develop according to a different pattern than that observed in the light. Moreover, synthesis of some proteins of the photosynthetic apparatus is inhibited. Light triggers the Pchlid photoreduction to Chlid, which induces the cascade of biochemical reactions and structural changes leading to the assembly of thylakoid membranes. In the present paper, the current knowledge on LPOR protein, mechanism of Pchlid to Chlid photoreduction, the role of lipid structure in etioplasts as well as spectral properties of Pchlid in etiolated seedlings and model systems is summarized.
"Pchl is more hydrophobic than Pchlide because of a long chain of phytol or its precursors attached to the tetrapyrrole ring (Fig. 1). The physiological role of Pchlide as an intermediate in chlorophyll biosynthesis has been known for a long time and intensively investigated (for a review see    ). In angiosperms, the reduction of Pchlide to chlorophyllide is catalysed by a photoenzyme, protochlorophyllide oxidoreductase (LPOR, EC.126.96.36.199). "
[Show abstract][Hide abstract] ABSTRACT: In the present work, a comparative study of protochlorophyllide- and protochlorophyll-lipid interaction was performed on liposomes prepared from phospholipids and galactolipids, which had a pigment content varying from 0.1 to 4 mol%. The incorporation of pigment molecules into the lipid bilayer and pigment-pigment interactions were investigated. Protochlorophyllide entered the lipid bilayer spontaneously and showed fluorescence spectra characteristic of its monomers. Similar spectra were observed for protochlorophyll where its concentration was low. However, the fluorescence maxima of protochlorophyll monomers were blue-shifted compared to those of protochlorophyllide by about 5 nm. Protochlorophyll at high concentrations formed transient aggregates that showed an additional fluorescence band with a maximum at around 685 nm, especially in liposomes prepared from phospholipids. For both compounds, the Stern-Volmer constant for KI quenching was much lower in liposomes than in solution, which confirmed the incorporation of these compounds into the lipid bilayer. Two populations of protochlorophyll that differed in their accessibility to quenching by KI were determined, and the proportions between them for different lipids is discussed. Protochlorophyllide showed such heterogeneity only in DPPC membranes. Quenching with 5- and 16-SASL revealed a localization of the porphyrin ring of both Pchl and Pchlide in the polar headgroup area of the lipid bilayer. The side chain of protochlorophyll forced these molecules to localize deeper in the bilayer in the case of DPPC in gel phase.
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