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K Colbow

Publications and source records attributed to K Colbow.

14 recordsLinked to original sources
PubMed1986

Oxygen exchange in ulva using a bare platinum electrode with 4 microsecond saturating light flashes.

Illuminating algae (Ulva species) on a bare platinum electrode with 4 microseconds of saturating light flashes leads to the familiar four-step oscillatory pattern of O(2) exchange. However, it appears that this O(2) exchange is a composite of O(2) evolution and endogenous O(2) uptake in the algae. We have added the O(2) uptake component to the O(2) exchange curve in order to obtain the corrected O(2) evolution flash sequence which shows a similar four-step oscillation as reported previously, but with negligible damping over the first three oscillations.

Journal Article↗
PubMed1983

Electron Transport-Dependent Chlorophyll-a Fluorescence Quenching by O(2) in Various Algae and Higher Plants.

A comparison of chlorophyll-a fluorescence in brown algae (Macrocystis integrifolia, Fucus vesiculosis), green algae (Scenedesmus obliquus, Ulva sp.) and higher plants (bean, corn) show differences in the relative fluorescence intensities and induction time courses which characterize each type of plant. These differences are not reflected in either the maximum fluorescence emission in the presence of 3-(3,4-dichlorophenyl)-1,1-dimethylurea (F(max)) or the nonvariable fluorescence (F(o)). Constancy of F(o) and F(max) suggests functional similarities of photosystem II and associated antennae pigments in the various classes of plants. The time course differences are observed only in the absence of 3-(3,4-dichlorophenyl)-1,1-dimethylurea and appear, therefore, to be electron transport dependent. During induction, the peak in fluorescence (F(p)) is much lower in all of the algae studied than in the higher plants. Exogenous O(2) strongly quenches F(p) in all plants studied and our data indicate that the low F(p) in the algae can be partially accounted for by endogenous O(2) quenching.

Journal Article↗
PubMed1983

Evolution of o(2) in brown algal chloroplasts.

A METHOD IS DESCRIBED FOR THE ISOLATION OF PHOTOSYNTHETICALLY ACTIVE CHLOROPLASTS FROM FOUR SPECIES OF BROWN ALGAE: Fucus vesiculosis, Nereocystis luetkeana, Laminaria saccharina, and Macrocystis integrifolia. When compared to lettuce and spinach chloroplasts, the algal chloroplasts all showed lower activities for both photosystems II and I. Chloroplasts from all the plants produced H(2)O(2), with photosystem I functioning as the O(2) reductant in the light. In contrast to the green plants, however, brown algal chloroplasts strongly reduced O(2) under conditions where both photosystems II and I remain active. Relative variable fluorescence values were lower both in intact plants and chloroplasts of the brown algae than for either spinach or lettuce. It is suggested that although light harvesting activities appear similar in all the plants, details of electron transport in brown algae may differ from those of green plants.

Journal Article↗
PubMed1978

Turbidity changes of lipid vesicles near the phase transition temperature as an indication of fusion.

Sonicated liposomes of dipalmitoyl phosphatidylcholine show sharp turbidity changes on heating at two distinct temperatures. A decrease in turbidity at the lower temperature (approx. 37degrees C) is thought to be associated with the phase transition of small vesicles and a decrease at about 44 degrees C with larger vesicles or multilayer. An increase of turbidity between 38 and 43 degrees C is attributed to the fusion of small vesicles. The turbidity changes were studied under various modes of vesicle preparation to confirm the interpretation of the turbidity data. Alternate interpretations are discussed.

Chemical Phenomena↗
PubMed1976

Energy transfer in photosynthesis.

A theoretical model is presented to account for the physical mechanism of energy transfer from antenna molecules to the reaction centers in photosynthesis. The energy transfer is described by a generalized transport equation or "master equation". The solution of this equation for the proposed model gives a relationship between the antennae interaction energy and the transfer rate. The results are shown to be in agreement with inter-antenna transfer rates calculated from experimental fluorescence lifetimes. Previous theories were based either on the Förster mechanism, which is valid for very small interaction energies, or an exciton model valid for very large interactions, but experimental results seemed to indicate that the actual situation was intermediate between these two. The Förster theory and the exciton model are limiting cases of the master equation.

Electron Transport↗
PubMed1976

Light scattering and turbidity measurements on lipid vesicles.

The dynamic behaviour of model membranes in the form of sonicated liposomes in excess water was studied by means of 90 degrees C light scattering and turbidity measurements. Computer calculations based on the Rayleigh-Gans theory of light scattering were used to estimate the average size of lipid vesicles dispersed in water, taking into account the various structures of the vesicles. Normal reversible changes in the scattered light intensity and turbidity with temperature could be accounted for mainly by the changes in the refractive index of the lipid and irreversible anomalous changes were explained on the basis of fusion of smaller aggregated vesicles.

Binding Sites↗
PubMed1976

Analysis of temperature-jump chlorophyll fluorescence induction in plants.

A newly observed general chlorophyll fluorescence induction effect in plants is described. Fluorescence yield can rise through as many as four different phases (alpha, beta, gamma, ) in the dark, when intact cells or leaves are rapidly heated (within approx. 2.5 s) from 20 to 40-50 degrees C. An analysis of this temperature-jump fluorescence induction in Scenedesmus obliquus leads to the following: 1. Phase alpha is due to removal of S-quenching and appears to be related to heat deactivation of the water-splitting enzyme system. With prolonged heating, irreversibility of alpha upon recooling reflects irreversible damage to the water-splitting enzyme system. 2. beta is independent of the S-states and of the redox state of primary System II acceptor Q. It is suggested that beta parallels functional separation of Q from the System II trapping centre. This effect is highly reversible. 3. gamma and beta reflect reduction of primary System II acceptor Q by a heat-induced endogenous reductant, which is probably identical to hydrogenase. Critical temperatures for pronounced alpha and beta phases differ markedly in different plants. Possible correlations between temperature-jump fluorescence inductio, thylakoid membrane lipid composition, lipid phase transition and lipid-protein interactions are discussed.

Chlorophyll↗
PubMedDate not supplied

Temperature--jump chlorophyll fluorescence induction in plants.

In contrast to slower heating rates, a temperature jump reveals complex rise phases in the heat induced chlorophyll fluorescence emission increase in intact plants. Three rise phases have been detected which indicate the stepwise loss of different quenching mechanism of system II fluorescence. Two of the phases appear to reflect heat deactivation of the system II reaction centers, while the other may be associated with the induction of hydrogenase activity. Variations in Tmax of the jump, for the increase in different plant varieties, suggest a correlation with membrane lipid phase transitions affecting thylakoid membrane structure and the fluorescence increase.

Chlorophyll↗