After solubilization of photosynthetic membranes by digitonin, three main protein pigment complexes were isolated by electrophoresis with deoxycholate as detergent.The band with the slowest mobility, fraction 1, had PS 1 activity and was devoid of PS 2 activity. This fraction was four times enriched in P700 when compared with chloroplasts. Fraction 1 had little chl b, a long wavelength absorption maximum in the red, a maximum of low temperature emission fluorescence at 730nm, and a circular dichroism spectrum characteristic of PS 1 enriched fraction.Fraction 2 exhibited a PS 2 activity and no PS 1 activity. It was enriched five times in PS 2 reaction centre and had little chl b and carotenoids. The absorption maximum was at 674 nm and the low temperature fluorescence emission maximum was at 700 nm. Fraction 2 might be useful PS 2 enriched particle because of the great stability of this fraction with regard to photochemical activity and also rapidity and simplicity of its preparation.Fraction 3, which had the fastest migration, was devoid of photochemical activities; It was rich in chl b and had the fluorescence and the circular dichroism spectrum characteristic of an antenna complex.
A newly purified Photosystem (PS) I particle is described, with still active iron-sulfur acceptors: A, B and X. Apart from the apoprotein of P700, 3 other main polypeptides of this particle are located at 20, 17 and 10 kDa, and two minor ones are detectable at 16.5 and 8 kDa. Both in vivo "S labeling and carboxymethylation with iodo[r4C]acetate show that most of the cysteine residues are located in the 8-kDa band. The amino acid composition of this band reveals important common features with small iron-sulfur proteins of the ferredoxin type.Photosystem I Digitonin/deoxycholate particle Iron-sulfur protein "S labeling Amino acid composition Photosynthesis
Under precise conditions, SDS PAGE† allows purification of a photoactive P700-chla-protein complex from eucaryotic cells. The yield of P700 recovery is close to 100%. A total protein content equivalent to about 140 kD for one mole of P700 has been estimated by chemical analysis, and electrophoresis revealed the presence of two peptidic chains with MWs close to 65 kD. Photochemical and structural properties of this complex are given and compared with those of other complexes previously isolated.
By means of labelling experiments with δ-[(3)H]aminolevulinic acid (ALA) and SDS acrylamide gel electrophoresis the following results were obtained with plantlets of Zea mays L.: Protochlorophyllide is associated with two peptide chains of the molecular weights (MW) 21000 and 29000, thus forming two protochlorophyllide holochromes. Chlorophyll may be associated with four peptide chains of MW 21000, 25000, 29000 and 70000, forming four chlorophyll holochromes. When plantlets are transfrrred to light, protochlorophyllide is converted to chlorophyll but this remains associated with the peptide chains MW 21000 and 29000; in addition, chlorophyll is synthesized from unmetabolized ALA and associated with peptide chains MW 25000 and 70000. These conversions occur both in dark-grown plantlets and in green plantlets transferred to darkness and then again exposed to light, but in the latter considerably faster than in the former. The results suggest the existence of two pathways for the formation of chlorophyll holochromes, one requiring a dark period followed by light, the other occurring without a dark phase. Light may not only be required for photoconversion of protochlorophyllide to chlorophyll, but may also be involved in the regulation of the formation of the protein-pigment complexes.
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