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18 recordsLinked to original sources
PubMed1977

Chloroplast biogenesis. Net synthesis of protochlorophyllide from magnesium-protoporphyrin monoester by developing chloroplasts.

Developing chloroplasts were isolated from greening Cucumis cotyledons in a cofactor-enriched medium and were incubated in the dark with 14C-labeled and unlabeled magnesium-protoporphyrin monoester. The metabolic pools between protoporphyrin and protochlorophyllide were monitored spectrofluorometrically. The incorporation of the 14C label into protochlorophyllide was also determined. It was shown that magnesium-protoporphyrin monoester, a postulated intermediate of the chlorphyll biosynthetic pathway, was convertible into protochlorophyllide with relatively high yields. Since protochlorophyllide is the immediate precursor of chlorophyll a it was concluded that magnesium-protoporphyrin monoester was indeed an intermediate of the chlorophyll biosynthetic pathway.

Chlorophyll↗
PubMed1977

Chloroplast biogenesis. Net synthesis of protochlorophyllide from protoporphyrin IX by developing chloroplasts.

Developing chloroplasts were isolated from greening Cucumis cotyledons in a co-factor-enriched medium and were incubated in the dark with 14C-labeled and unlabeled protoporphyrin IX. The metabolic pools between protoporphyrin and protochlorophyllide were monitored spectrofluorometrically. The incorporation of the 14C label into protochlorophyllide was also determined. It was shown that protoporphyrin IX, a postulated intermediate of the chlorophyll biosynthetic pathway, was convertible into protochlorophyllide. Since protochlorophyllide is the immediate precursor of chlorophyll a it was concluded that protoporphyrin IX was indeed an intermediate of the chlorophyll biosynthetic pathway.

Chlorophyll↗
PubMed1979

Kinetics of photoconversion of protochlorophyllide 649 to chlorophyllide 676 at low temperature in etiolated cotyledons of Pharbitis nil.

The kinetics of the photoconversion of protochlorophyllide 649 to chlorophyllide 676 were studied spectrophotometrically over the temperature range of -15 -- -80 degrees C under light-saturating conditions in etiolated cotyledons of Pharbitis nil. Photoconversion obeyed the sum of two first-order kinetics over this low temperature range. Activation energies obtained from the rate constants were about 5000 cal; this suggests that these two processes may be physical processes not chemical reactions. The results indicate that photoconversion involves two main steps. One is the step dependent on both light intensity and temperature that has been well studied. The other, which is concerned in this study, is the step dependent on temperature only, which may be the requisite for photoconversion. This latter step seems to be related to the binding mode of protochlorophyllide to a holochrome protein or to conformational changes in the protochlorophyllide-holochrome.

Chlorophyll↗
PubMedDate not supplied

[Investigation of the initial steps of protochlorophyllide photoreduction in etiolated plants].

The irreversible nonfluorescent product of the protochlorophyllide photoreduction with the wide electronic band at 705 nm was discovered. The P705 product through the intermediate products with the fluorescence max at 695 nm and 687 nm turns into Chl684 678, as the result of heating in darkness. The P705, P695, P687 products quench protochlorophyllide fluorescence with great efficiency. Analysis of the intermediate product properties allow to propose a new photoreduction mechanism that includes energy transfer to the trapping center where the charge transfer is performed, nonradiative energy dissipation in the charge-transfer complex, and protonation and disproportionation of the pigment anion-radicals.

Chlorophyll↗
PubMed1978

Chloroplast culture: the chlorophyll repair potential of mature chloroplasts incubated in a simple medium.

The chlorophyll repair potential of mature Cucumis chloroplasts incubated in a simple Tris-HCl/sucrose medium is described. The chloroplasts were isolated from green, fully expanded Cucumis cotyledons which were capable of chlorophyll repair. This was evidenced by a functional chlorophyll biosynthetic pathway in the mature tissue. The biosynthesis of protocholorphyllide from exogenous delta-aminolevulinic acid was used as a marker for the operation of the chlorophyll biosynthetic chain between delta-aminolevulinic acid and protochlorophyllide. The conversion of exogenous protochlorophyllide into chlorophyll a was used as a marker for the operation of the chlorophyll pathway beyond protochlorophyllide. It appeared from these studies that contrary to published reports, unfortified fully developed Cucumis chloroplasts incubated in Tris-HCl/sucrose without the addition of cofactors exhibited a partial and limited chlorophyll repair capability. Their net tetrapyrrole biosynthetic competence from delta-aminolevulinic acid was confined to the accumulation of coproporphyrin. No net tetrapyrrole biosynthesis beyond coproporphyrin was observed. However, the plastids were capable of incorporating small amounts of delta-amino[4-(14)C]levulinic acid into [14C]protochlorophyllide but were incapable of converting exogenous protochlorophyllide into chlorophyll. After prolonged incubation of the unfortified chloroplasts in the dark, a fluorescent protochlorophyllide-like compound accumulated. This compound [Cp (E430-F631) was shown to be neither protochlorophyllide nor zinc-prototochlorophyllide but and a fluorescence emission maximum at 631 nm (F631) in methanol/acetone (4 : 1, v/v). Cp(E430-F631) WAS SHOWN TO BE NEITHER PROTOCHLOROPHYLLIDE NOR ZINC-PROTOTOCHLOROPHYLLIDE BUT an enzymatic degradation product of chlorophyll. The exact chemical identity of this compound has not yet been determined.

Cells, Cultured↗
PubMed1978

Reconstitution of chlorophyllide formation by isolated etioplast membranes.

1. The reconstitution of chlorophyllide biosynthesis by barley etioplast membranes is described. 2. The process is dependent on the additon of NADPH and protochlorophyllide and on illumination, which can be either continuous or intermittent. 3. The reconstituted process involves spectroscopically similar intermediates to the native reaction in whole leaves. 4. Steps in the process are an initial enzymic formation in the dark of a photoactive complex, P638/652 (probably a ternary protochlorophyllide-NADPH-enzyme complex), followed by a very rapid light-dependent hydrogen transfer from the NADPH to the protochlorophyllide giving chlorophyllide giving chlorophyllide, finally releasing the enzyme for repeating the process. 5. A continuous assay for the system regenerating complex P638/652 was devised on the basis of monitoring chlorophyllide formation. 6. The pH optimum of the reaction is at 6.9 and Km values for protochlorophyllide and NADPH are 0.46 and 35 micron respectively. 7. The reaction is associated specifically with the etioplast membrane fraction. 8. Activities of the system assayed in vitro are more than adequate to account for rates of chlorophyll formation in vivo.

Chlorophyll↗
PubMed1979

[Effects of organic solvent vapors on the protochlorophyllic complex from etiolated leaves. Conditions for reversible and irreversible destruction].

The spectral properties and the ability of etyolated leaves pigments treated with organic solvent vapours (OS) for phototransformations were studied by measuring low temperature fluorescence spectra (-196 degrees C). Under the effects of OS the fluorescence at 655 nm was gradually decreased and that at 630--640 nm was increased. The effects of OS depended on the partial pressure of OS. The ability of the pigments for phototransformations was decreased with an increase in fluorescence at 630 nm. The emission maximum of fluorescence of the pigment formed in the light was shifted by 10--18 nm towards the shortwave region. Partial reversibility of the destroying effects of diethyl ester was found. A removal of the ester vapours resulted in a relative increase of fluorescence in the etyolated leaves at 640--645 nm and a decrease of the amount of "photo-inactive" pigment. The maximum of fluorescence of the pigment formed in the light was shifted towards the long-wave region (approximately 5 nm) as compared to the leaves irradiated in the presence of the ester. Partial functional reconstitution indicates that at least part of the pigment molecules are able to form a protochlorophyllide (protochlorophyll) -- protein complex, similar to the native one.

Chlorophyll↗
PubMedDate not supplied

[Relationship between chlorophyll concentration and the energy reaction between protochlorophyll and chlorophyll in mixed associations].

In the paper results are presented of investigation of protochlorophyll (PChl) and chlorophyll (Chl) mixed associations and of interaction between them within the polymer molecular complex, which forms in mixture of water-dioxane (1 : 4). The initial PChl concentration in all solutions was constant (CPChl = 1 . 10(-5) m/l), and Chl concentration varied from 1.10(-8) m/l up to 2.10(-5) m/l. It is shown that with the rise of Chl proportion in the mixed aggregate the rearrangement of both donor (PChl) and acceptor (Chl) components of complex takes place. The luminescence quenching of PChl and the sensitization of Chl emission in mixed pigment associates were investigated of different Chl levels and the evaluation of efficiency of intracomplex electronic excitation energy transfer, determined from quenching and sensibilization, was performed. Similar dependence of energy transfer effectiveness on Chl concentration, determined by the two above-mentioned methods shows that the excitation migration in an associate takes place without losses. An analysis of results permits to conclude that a small trapping efficiency of PChl excitation by the acceptor part of the complex may be connected with the existence of the prerelaxation reverse energy transfer from Chl to PChl in mixed pigment associates. On the basis of the obtained data a mechanism of energy transfer from protochlorophyllide to chlorophyllide in etiolated leaves and homogenates is discussed.

Binding Sites↗
PubMed1976

Kinetics and regulation of synthesis of the major polypeptides of thylakoid membranes in Chlamydomonas reinhardtii y-1 at elevated temperatures.

Etiolated cells of Chlamydomonas reinhardtii y-1 exhibit rapid and linear initial kinetics of greening when exposed to light at 38 degrees C. The initial rate of chlorophyll accumulation under these conditions is greater than the maximal rate during greening at 25 degrees C. Synthesis of the major polypeptides of thylakoid membranes within intact cells was assayed during greening by the incorporation of [3H]leucine and the subsequent electrophoresis of total cellular protein on polyacrylamide gels in the presence of sodium dodecyl sulfate. At 38 degrees C the major membrane polypeptides (about 28,000 and 24,000 daltons in mass) were synthesized at a linear rate after exposure of the cells to light, with no evidence of a lag period. A 1-2 h preincubation in the dark at the higher temperature was necessary to achieve linear initial kinetics. Actinomycin D inhibited synthesis of the membrane polypeptides if added at the beginning of a 2 h dark preincubation, but not when added near the end. These results suggested that transcription of the messenger RNA for the membrane polypeptides occurred during the dark period at 38 degrees C. But the major membrane polypeptides were not made by y-1 cells in the dark. The wavelengths of light most effective in eliciting production of the membrane polypeptides were the same as those allowing chlorophyll synthesis. In contrast, wild type cells, which are capable of chlorophyll synthesis in the dark, also make the membrane polypeptides in the dark. The data indicate that at elevated temperatures synthesis of the major thylakoid membrane polypeptides is controlled at a posttranscriptional step, and that this reaction normally proceeds only under conditions which permit reduction of protochlorophyllide.

Amino Acids↗
PubMed1977

The dimerization of protochlorophyll pigments in non-polar solvents.

The infrared, visible and nuclear magnetic resonance spectra of protochlorophyll a and vinylprotochlorophyll a in dry non-polar solvents (carbon tetrachloride, chloroform, cyclohexane) are presented and interpreted in terms of dimer interaction. The infrared spectra in the 1600-1800 cm-1 region clearly show the existence of a coordination interaction between the C-9 ketone oxygen function of one molecule and the central magnesium atom of another molecule. Infrared spectra in the OH stretching region (3200-3800 cm-1) provide a valuable test of the water content in the samples. The analysis of the absorption and circular dichroism spectra of protochlorophyll a and vinylprotochlorophyll a in carbon tetrachloride demonstrates the existence of a monomer-dimer equilibrium in the concentration range from 10(-6) to 5.10(-4) M. The dimerization constants are (6 +/-2).10(5)1.M-1 for protochlorophyll a and (4.5 +/-21.10(5) 1.M-1 for vinylprotochlorophyll a at 20 degrees C. The deconvolution of visible spectra in the red region has been performed in order to obtain quantitative information on the dimer structure. Two models involving a parallel or a perpendicular arrangement of the associated molecules are considered. From 1H NMR spectra, it appears that the region of overlap occurs near ring V, in agreement with the interpretation of the infrared spectra.

Chemical Phenomena↗
PubMed1975

Characterization of the terminal stages of chlorophyll (ide) synthesis in etioplast membrane preparations.

1. Chlorophyll (ide) formation from protochlorophyll (ide) that is normally inactive was demonstrated in etioplast membranes isolated from maize and barlley plants, the process being dependent on intermittent illumination and the addition of NADPH. 2. The addition of NADPH to the membranes was shown to result in the conversion of inactive protochlorophyll (ide) absorbing at about 630 nm into a form(s) with light-absorption maxima at about 640 and 652 nm, both of which disappear when chlorophyll (ide) is formed on illumination. 3. The temperature-dependence of the activation process and its response to a variety of reagents were examined. From these, the conclusion is drawn that -SH groups are involved in the activation but in the active complex these are unavailable for reaction with -SH reagents. 4. Evidence is presented for the occurrence of glucose 6-phosphate dehydrogenase activity within etioplasts and the suggestion is made that the oxidative pentose phosphate pathway can provide the NADPH required for chlorophyll biosynthesis during the early stages of greening.

Cell Membrane↗
PubMedDate not supplied

[Spectral-luminescent properties of separate aggregated forms of pigments in solutions].

The aggregated forms of protochlorophyll a (PChl), 4-vinyl-protochlorophyll a (4VPChl) and chlorophyll a (Chl) in binar mixtures of dioxane-water was investigated. The aggregates are oligomer particles of pigment molecules having considerable degrees of fluorescence polarisation which points to their ordered structure. Two types of fluorescent associates I and II have been discovered. By its electronic spectrum I is similar to the molecular pigment but has smaller quantum yield B congruent to 10(-2) and the lifetime of fluorescence tau congruent to 3--4.10(-9) sec. Associates of type I spontaneously transform into associates of type II which have narrower bands of electronic spectrum than the monomer, very low B congruent to 10(-3)--10(-4) and tau congruent to 2--4.10(-10) sec. In contrast with the decreasing of B and the band intensities in CD spectrum conditioned by rotational strength increase by factor of 100 under transformation from I to II. It follows from these data that the antibatic connection possibly exists between excitation deactivation in associates and their optical activity. From data on splitting the associate CD spectra of type I and II the excitation interaction energy V12 congruent to 75 cm-1 was estimated. The reasons of increasing of rotational strength under transformation from I to II and the overturn of the sign dependence of bands in CD spectrum in some cases are discussed.

Chlorophyll↗
PubMedDate not supplied

[Photoluminescence of singlet oxygen in solutions of chlorophylls and pheophytins].

With the use of mechanical phosphoroscopes the photoinduced luminescence of singlet oxygen (1270 nm) have been found in air saturated solutions of chlorophyll a, bacteriochlorophyll a, protochlorophyll and pheophytins in CCl4, CS2, and freon 112. The excitation spectra of the luminescence coincide with the absorption spectra of the pigments. The relative quantum yields of the luminescence are determined, the data are used for calculation the probablities of intersystem crossing in pigment molecules. All the pigments are shown to quench 1O2, the rate constants of the quenching are measured. The quenching efficiency of the chlorophylls increases with reduction of the semiisolated double bonds, reduction of these bonds in molecules of the pheophytins decreases the constants of the quenching.

Bacteriochlorophylls↗