Photosynthetic Membrane System Research Articles

Isolation and Characterization of a Bacteriochlorophyll-containing Protein from Rhodopseudomonas spheroides

Abstract Polyacrylamide gel electrophoresis of the major protein-containing fraction of Rhodopseudomonas spheroides chromatophores reveals the presence of five electrophoretic components. The predominant component has associated with it, nearly all of the chlorophyll and phospholipid initially present in the chromatophore. Because of its potential structural and functional importance, this fraction has been isolated and purified by sodium dodecyl sulfate (SDS) preparative acrylamide gel electrophoresis. As isolated from preparative gels, this protein is at least 95% pure by virtue of the following criteria: protein chemistry, analytical gel electrophoresis, immunochemical reactivity, and a linear sedimentation-equilibrium plot. Chemical characterization of the protein-lipid-pigment complex reveals the presence of approximately 59% protein, 35% phospholipid, and 6% chlorophyll. Amino acid analysis of the purified protein shows a high content of nonpolar residues, no histidine or cysteine. Minimum molecular weights were estimated as 7,000 by amino acid analysis, 10,000 by SDS-acrylamide gel analysis, and 15,000 by sedimentation equilibrium analysis. Immunochemical characterization indicates that this protein is specific to only the photosynthetic membrane system derived from phototrophically grown cells.

P700 oxidation and energy transfer in normal maize and in carotenoid-deficient mutants

1. Particles enriched in System 1 and 2, respectively, were prepared by digitonin fragmentation of chloroplasts from normal maize and from mutants which accumulate lycopene or ζ-carotene instead of the normal carotenoids and which have a reduced chlorophyll content. Although both mutants had a relatively high carotenoid content in relation to chlorophyll, the System-1 particles showed about the same carotenoid to chlorophyll ratio as particles from normal maize. Particles from the lycopene mutant showed approximately a normal ratio of light harvesting to reaction center chlorophyll (P700). In the ζ-carotene mutants the amount of light harvesting chlorophyll was somewhat reduced, both in relation to the number of System-1 reaction centers and to the amount of protein. 2. Action spectra for P700 oxidation indicate a 30–50% efficiency of energy transfer from carotenoids to chlorophyll in System-1 particles of normal maize, increasing with increasing chloroplast development during greening. With the lycopene mutant the transfer efficiency was 30–50%. In the ζ-carotene mutant the transfer efficiency from ζ-carotene was estimated to be somewhat higher. The quantum efficiencies for P700 oxidation for light absorbed by chlorophyll a by System-1 particles from mutant maize were about twice as low as for normal maize. 3. With normal maize, after prior etiolation, the formation of functional System-1 reaction centers lags behind the synthesis of chlorophyll in the early phases of greening. Approximately at the time of beginning of granum formation, when about 20% of the chlorophyll had been synthesized, the ratio of chlorophyll to P700 and the distribution of chlorophyll between the two pigment systems was found to reach a constant value, suggesting a close relation between the regulatory mechanisms for these phenomena and the development of the photosynthetic membrane system.

Photosynthetic membrane system in Anacystis nidulans.

Cultures of Anacystis nidulans were grown under conditions of varying light intensity and temperature. Changes in pigment content were compared with changes in the fine structure of these cells. Pigment concentration and lamellar content varied inversely with the light intensity in cells grown with 100 and 1,000 foot candles of fluorescent light. Estimations of the relative area and volume of lamellae in cells showed that the amount of double membrane was directly proportional to the chlorophyll content of whole cells. Continuity of double membranes with cytoplasmic membrane was observed.