Phototransformation of Aggregated Forms of Protochlorophyllide in Isolated Etioplast Inner Membranes

Abstract

Irradiation of an etioplast inner membrane fraction caused the transformation of two photoactive spectroscopically different protochlorophyllide forms into two chlorophyllide forms. A weak light flash, 6% of a saturating Hash, preferentially caused the formation of a short wavelength chlorophyllide form absorbing at 672 nm and emitting at 676 nm. A saturating flash resulted in the formation of the 684 nm absorbing form of chlorophyllide with an emission maximum at 698 nm.The circular dichroism (CD) signals of the newly formed chlorophyllide forms indicated that thcy are pigment aggregates of different sizes. These aggregates are probably connected to protochlorophyllide reductase and NADPH or NADP. In the absence of NADPH a decomposition of the pigment aggregates took place as revealed by a decrease in the CD-signal. A model is suggested which describes the structural changes of the pigment-protein aggregates after irradiation.

The influence of glycerol and chloroplast lipids on the spectral shifts of pigments associated with NADPH:protochlorophyllide oxidoreductase from Avena sativa L

“…If the incubation is performed in darkness, the shift is accompanied by a regeneration of photoactive Pchlide absorbing at 650 nm. Several explanations for the Shibata shift, based on indirect evidence, have been o¡ered by some authors, but questioned by other authors (for the Shibata shift), including esteri¢cation of newly formed Chlide a [18], displacement of Chlide a from the POR^product complex [14], and disaggregation of large enzyme^product aggregates into smaller ones [16,19], possibly connected with dephosphorylation of the POR^product complex [15].…”

Protochlorophyllide oxidoreductase B-catalyzed protochlorophyllide photoreduction in vitro : Insight into the mechanism of chlorophyll formation in light-adapted plants

“…At least three different spectral forms of PChlide are recognized in intact tissues based on their fluorescence emission maximum (in nm): PChlide F632, PChlide F644, and PChlide F655 (5). The main photoactive form present in etiolated plants is PChlide F655, which, after illumination, is converted to Chlide and, subsequently, to chlorophyll (F682) through the formation of several, long wavelength intermediates (5)(6)(7)(8)(9). In most angiosperms, POR and its substrate localize to specific structures termed prolamellar bodies that are not detected in light-adapted plants (10).…”

The effects of low pH on the properties of protochlorophyllide oxidoreductase and the organization of prolamellar bodies of maize (Zea mays)

“…A number of lines of evidence suggest that POR-PChlide 640 and PORPChlide 650 are the less and more aggregated forms, respectively, of the same enzyme [1,[6][7][8] and Ryberg, Sundqvist and their coworkers [9][10][11] have recently reported results suggesting that this aggregation may be favoured by POR phosphorylation. The idea of a possible phosphorylation step in the interconversion of different forms of POR can be traced back to an early series of experiments by Horton & Leech [14,15] in which the transformation of PORPChlide 650 to a short-wavelength form with an absorption maximum around 630 nm in aged maize etioplasts was found to be reversed by the addition of ATP.…”

“…The PLB membrane is dominated by the presence of a single protein species, protochlorophyllide oxidoreductase (EC 1.3.1.33) (POR) that catalyses the light-driven, NADPH-dependent reduction of protochlorophyllide (PChlide) to chlorophyllide (Chlide). Analyses of the absorption spectrum of PLB [1] and low-temperature fluorescence spectra of etioplast inner membrane preparations (EPIM) and PLB [2], indicate the presence of three major pools of PChlide; a nonphotoconvertible form PChlide 628)633 and two photoconvertible forms PChlide 640)645 and PChlide 650)657 . The suffix numbers relate to the wavelengths of the absorption and emission maxima, respectively.…”

“…A number of lines of evidence suggest that POR-PChlide 640 and PORPChlide 650 are the less and more aggregated forms, respectively, of the same enzyme [1,[6][7][8] …”