Solubilization of chloroplast membranes by zwitterionic detergents

Thirty years of fun with antenna pigment-proteins and photochemical reaction centers: A tribute to the people who have influenced my career

The author summarizes the research contributions to photosynthesis made by him, his graduate and postdoctoral students, visiting scientists and by his collaboration with other photosynthesis workers during 1964-1994. The development of isolation procedures and biochemical/biophysical characterization of antenna pigment-proteins and photochemical reaction centers are described together with the author's education and experiences as a scientific researcher. Some anecdotes hopefully add insight into what it was like to be in this area of science during the period.

Chlorophyll-protein organization of membranes from the cyanobacterium Anacystis nidulans

Six chlorophyll-containing bands were observed upon electrophoretic analysis of Anacystis nidulans thylakoid membranes. These ranged in apparent molecular weights from approximately 360 to 45 kdalton. Measurements of the light absorption and chlorophyll fluorescence properties of these bands revealed numerous differences among the aggregates. The larger chlorophyll-protein complexes had a chlorophyll absorption maximum at 676 nm while the smallest band, band VI, at approximately 45 kdalton, absorbed at 668 nm. The chlorophyll-protein organization of four submembrane particles was also examined. Digitonin and N-tetradecyl-N,N-dimethyl-3-ammonio-1-pro-panesulfonate were used to fractionate thylakoids and each treatment yielded two green fractions after sucrose density gradient centrifugation. The upper green fractions of both procedures were enriched in band VI. In addition, these fractions showed low temperature fluorescence emission at 686 nm. Conversely, the lower green fractions were enriched in the larger bands (bands I and II), and yielded fluorescence emission at 696 and 716 nm. The gel electrophoresis analysis of these chlorophyll-protein bands revealed 11 peptides ranging in size from less than 10 to 64 kdaltons. The larger CP bands contained as many as five to six polypeptides, whereas band VI contained only two species (at 45 and 48 kdalton). These data suggest that the only proteins in band V (approximately 75 kdalton) and band VI are the chlorophyll binding proteins for photosystems I and II, respectively. We present a model which correlates chlorophyll-protein organization and specific fluorescence emission peaks. Central to this model is the interaction of the larger chlorophyll-protein complexes with bands V and VI to yield fluorescence at 696 and 716 nm, respectively. In addition, the polypeptide composition of each complex allows us to construct a topological model of these complexes within the Anacystis thylakoid.

Isolation and characterization of cytoplasmic membranes and chlorosomes from the green bacterium Chloroflexus aurantiacus

A method was developed which allows the isolation and purification of cytoplasmic membranes and chlorosomes from cells of Chloroflexus aurantiacus grown under different light conditions. The dipolar ionic detergent Deriphat (0.08%) and a sodium iodide gradient centrifugation were used in isolating cytoplasmic membranes. Chlorosomes were prepared with 0.16% of the dipolar ionic detergent Miranol and purified by a sucrose gradient centrifugation. Cytoplasmic membrane fractions prepared from either high- (3,000 W m-2), medium-(200 W m-2) or low- (7 W m-2) light-grown cells had near infrared absorption bands at 866, 808, and 755 nm in a constant characteristic absorbance ratio of 6:3.8:1. In all cytoplasmic membrane preparations, the amount of bacteriochlorophyll a (Bchl a) per cytochrome, the amount of Bchl a per reaction center, and reaction center per milligram of cytoplasmic membrane protein was found to be constant. No Bchl c was present. Five respiratory enzyme activities have been measured in the cytoplasmic membrane fraction. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of denatured cytoplasmic membrane showed many bands, but a major polypeptide with an apparent molecular weight of 8,000. In contrast, sodium dodecyl sulfate-polyacrylamide gel electrophoresis of purified chlorosomes did not contain the 8,000-molecular-weight band but revealed only three distinct protein bands with molecular weights of 15,000, 12,000, and 6,000. Isolated chlorosomes contained Bchl c and a small, yet constant, amount of Bchl a (absorbing at 790 nm) in a molar ratio of 25:1. The data indicated that the components of the photosynthetic apparatus in the cytoplasmic membrane of Chloroflexus aurantiacus remained constant and only the amount of antenna Bchl c varied with light conditions.

Effect of detergents on the reliability of a chemical assay for P-700

A chemical assay for P-700 was developed using 0.36 mM potassium ferricyanide as oxidant and 1.6 mM sodium ascorbate as reductant. The major difference from other chemical assays for P-700 is procedural. The method is designed to take advantage of the availability of microprocessor-linked spectrophotometers to obtain greater accuracy by minimizing the spectral changes due to irreversible oxidized antenna chlorophyll molecules. The value measured for the P-700 concentration in a sample of chloroplasts was not changed by the presence of EDTA, Mg2+ or sucrose in the assayed solution. Similarly, half of the detergents tested (Triton X-100, Nonidet P-40, digitonin, Deriphat 160, Miranol S2M-SF and Miranol M2M) did not alter the value when added to the chloroplasts. The remainder of the detergents examined caused a significant decrease or increase in the value for P-700 content. Sodium dodecyl sufate, of particular interest due to its widespread use, caused a doubling in the amount of apparent P-700. This effect may be due to this detergent and some others enabling an additional long wavelength form of chlorophyll, possibly an intermediary electron acceptor in Photosystem I, to be chemically oxidized and reduced under the assay conditions.