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Biomedical subjects

R A Dilley

Publications and source records attributed to R A Dilley.

At least 73 records · Page 4Linked to original sources
PubMed1972

Biochemical and Biophysical Characteristics of a Photosynthetic Mutant of Euglena gracilis Blocked in Photosystem II.

A photosynthetic mutant of Euglena gracilis, Z strain, thought to be blocked in the electron transport chain between the two photosystems and to have a missing or nonfunctional primary acceptor for photosystem II, was further studied and characterized. The data from low temperature fluorescence spectra, delayed light emission, and electron paramagnetic resonance support the previous work.The mutant was shown to lack plastoquinone A and possibly cytochrome b(559) but to possess plastoquinone B and a higher complement of carotenoids, especially xanthophylls, than the wild type.The results are consistent with the postulated role of plastoquinone as the primary electron acceptor for photosystem II and as responsible for the electron paramagnetic resonance signal II. The abundance of xanthophylls in the mutant can be explained by the protective role of carotenoids against photosensitized reactions.

Journal Article↗
PubMed1972

Structural Characteristics of a Photosynthetic Mutant of Euglena gracilis Blocked in Photosystem II.

The techniques of thin sectioning and freeze etching were employed in comparing the chloroplast structure of the wild type and photosynthetic mutant P(4) of Euglena gracilis, Z strain. The mutant chloroplasts were characterized by a lack of thylakoid pairing even under high salt conditions. In addition the mutant thylakoids were more varied in size and fewer in number than those of the wild type. No differences between the mutant and wild type were observed in the size and distribution of the particles within the chloroplast membranes seen by the freeze-etching technique.These structural abnormalities do not appear to be correlated per se with the absence of plastoquinone A in the mutant but may be related to a different lipid composition observed in the mutant.

Journal Article↗
PubMed1970

The relation of the 515 nanometers absorbance change to adenosine triphosphate formation in chloroplasts and digitonin subchloroplast particles.

The flash-induced absorbance changes at 515 nanometers has been studied in chloroplasts and in digitonin subchloroplast particles of lettuce. The effect of various conditions and uncouplers was tested on the decay kinetics of this absorbance change and on ATP formation in the presence of phenazine methosulphate, either by continuous or flash illumination. It has been found that in chloroplasts, carbonyl cyanide m-chloromethoxyphenylhydrazone and nigericin in the presence of K(+) accelerate the decay of the 515 change and inhibit ATP formation. However, under a variety of conditions the rate of decay of the 515 absorbance change was found to be unrelated to ATP formation. Preillumination, addition of valinomycin in the presence of K(+), addition of Na(+), or divalent cations accelerate the decay of the 515 absorbance change markedly but have no effect on ATP formation. Addition of phosphorylation reagents has no effect on the decay rate beyond that obtained by Mg(2+) and inorganic phosphate. NH(4)Cl, and to some extent atebrin, while inhibiting ATP formation, do not affect the decay of the 515 absorbance change.In digitonin subchloroplast particles the decay kinetics of the absorbance change resemble that of chloroplasts, but the magnitude of the change is smaller. The pH change in this preparation is reduced much more than the 515 absorbance change.According to the chemiosmotic hypothesis, the sum of DeltaE(membrane potential) and DeltapH is the driving force for ATP formation. The lack of an increase in DeltaE in digitonin subchloroplast particles, which are practically devoid of DeltapH and have a normal ATP-forming activity, is inconsistent with the chemiosmotic hypothesis.

Journal Article↗
PubMed1970

Chloroplast composition and structure differences in a soybean mutant.

A nuclear mutation of Glycine max (soybean) segregates 1:2:1 in regard to chlorophyll content. The heterozygous (LG) leaf blade contains about one-half the pigment content of the wild type (DG) per gram fresh weight. A lethal yellow (LY) type contains about 1 to 2% of the DG leaf pigment values. The chlorophyll a/b ratio in the LG is about 5 compared to about 2 in the DG. Protein/leaf values are lower in the LG and LY types when compared to DG. The LG plastid lamellae contain more protein/chlorophyll, cytochromes/chlorophyll, and quinones/chlorophyll than the DG. P(700)/chlorophyll values are similar in the DG and LG types.The chlorophyll-depleted LG and LY types had less total acyl lipids per leaf weight when compared to the DG type. Similar amounts of sulfolipid and phosphatidyl glycerol per protein residue weight were found in the LG and DG plastids; however, the monogalactosyl and digalactosyl diglycerides were reduced in the LG paralleling the chlorophyll depletion.Thin sections of leaf tissue show similar-sized LG and DG plastids but reduced grana formation in the LG. The LY has very few grana and very small grana compared to either DG or LG. The two characteristic particles revealed in higher plant chloroplasts by freeze-etching are about 15% smaller in the LG compared to the DG plants.

Journal Article↗
PubMed1970

Photochemical characteristics in a soybean mutant.

Chloroplasts were isolated from wild type (DG) and heterozygous mutant (LG) soybean (Glycine max) leaves, and various biochemical functions were compared. Noncyclic electron transport, and its coupled phosphorylation, cyclic phosphorylation and H(+) ion transport in both systems, were 3 to 5 times faster in rate (on a chlorophyll basis) in the mutant plastids. On a chloroplast lamellar protein basis, the mutant plastid rates were 1.5 to 2.5 times the wild type rates.Plastoquinone (PQ) reduction and oxidation (rates and extent) were measured by following absorbance changes at 260 nanometers with the repetitive flash technique. Mutant plastids have about a 2-fold greater apparent first order rate constant for PQ oxidation and a 3- to 5-fold larger pool of rapidly reducible PQ. Plastoquinone oxidation has been identified by other workers as the rate-limiting step in electron transport. Assuming the PQ oxidation is a first order process (d(PQH(2))/dt = k(D)[PQH(2)]t), the observed increase in k(d) for the LG (k(d) (LG) approximately 2k(d) (DG)) and the greater steady state amount of rapidly turning over PQ, [PQH(2)](LG)>[PQH(2)](DG), could account for the 3- to 5-fold greater rates of electron transport and phosphorylation found in the mutant chloroplasts.Light saturation for noncyclic photophosphorylation and photosystem 2 plus 1 electron transport occurred at similar intensities for both LG and DG plastids. Relative quantum requirements extrapolated to zero intensity were similar in the LG and DG, although at finite light intensities the LG had a better relative quantum efficiency.Ammonium chloride concentrations needed to inhibit cyclic photophosphorylation 50% were similar in both LG and DG plastids. Nigericin, poly-l-lysine, and chlorotri-n-butyltin, were needed in concentrations 5 to 10 times greater in the LG to yield 50% inhibition at comparable chlorophyll concentrations.

Journal Article↗
PubMed1969

A comparison of chloroplast membrane surfaces visualized by freeze-etch and negative staining techniques; and ultrastructural characterization of membrane fractions obtained from digitonin-treated spinach chloroplasts.

Spinach chloroplast lamellae were washed free of negatively staining surface particles (carboxydismutase and coupling factor protein) and the resulting smooth-surfaced lamellae still showed the usual large (175 A) and small (110 A) particles seen by freeze-etching. Therefore, the freeze-fracture plane probably occurs along an internal surface of the chloroplast membrane. Fractions obtained by differential centrifugation of digitonin-treated chloroplast membranes were studied by negative staining, thin sectioning, and freeze-etching techniques for electron microscopy. The material sedimenting between 1,000 g and 10,000 g, enriched in photosystem II activity, was shown to consist of membrane fragments. These freeze-etched membrane fragments were found to have large particles on most of the exposed fracture faces. The large particles had the same size and distribution pattern as the 175 A particles seen in intact chloroplast membranes. The material sedimenting between 50,000 g and 144,000 g, which had only photosystem I activity, was found to consist of particles in various degrees of aggregation. Freeze-etching of this fraction revealed only small particles corresponding to the 110 A particles seen in intact chloroplasts. A model is presented suggesting that chloroplast lamellar membranes have a binary structure, which digitonin splits into two components. The two membrane fragments have different structures, revealed by freeze-etching, and different photochemical and biochemical functions.

Cell Membrane↗