Carotenoid-to-bacteriochlorophyll energy transfer through vibronic coupling in LH2 from <Emphasis Type="Italic">Phaeosprillum molischianum</Emphasis>

The peripheral light-harvesting antenna complex (LH2) of purple photosynthetic bacteria is an ideal testing ground for models of structure–function relationships due to its well-determined molecular structure and ultrafast energy deactivation. It has been the target for numerous studies in both theory and ultrafast spectroscopy; nevertheless, certain aspects of the convoluted relaxation network of LH2 lack a satisfactory explanation by conventional theories. For example, the initial carotenoid-to-bacteriochlorophyll energy transfer step necessary on visible light excitation was long considered to follow the Förster mechanism, even though transfer times as short as 40 femtoseconds (fs) have been observed. Such transfer times are hard to accommodate by Förster theory, as the moderate coupling strengths found in LH2 suggest much slower transfer within this framework. In this study, we investigate LH2 from Phaeospirillum (Ph.) molischianum in two types of transient absorption experiments—with narrowband pump and white-light probe resulting in 100 fs time resolution, and with degenerate broadband 10 fs pump and probe pulses. With regard to the split Q_x band in this system, we show that vibronically mediated transfer explains both the ultrafast carotenoid-to-B850 transfer, and the almost complete lack of transfer to B800. These results are beyond Förster theory, which predicts an almost equal partition between the two channels.     

The application of laser microprobe mass analysis to the study of biological material

Laser microprobe mass analysis (LAMMA) is an investigational method which is a powerful tool for the identification and quantitation of various elements present in small volumes of tissue. LAMMA is highly sensitive and capable of rapidly detecting concentrations of 1–3 p.p.m. of most metallic elements, in precisely localized cellular compartments. In order to further assess its value, cultured skin fibroblasts and biopsy tissues from human subjects and experimental animals were probed by LAMMA, and the results were correlated with ultrastructural findings. Biopsy samples were obtained from patients suffering from Gaucher disease, and from patients and animals with pathologic iron or copper metabolism. No significant abnormalities were detected in the cultured fibroblasts from patients with Gaucher disease, in contrast to the iron content of tissue biopsy Gaucher cells, which was markedly increased, apparently as a consequence of erythrophagocytosis. Particularly intense iron-related peaks were found in liver cytosiderosis due to neonatal or genetic haemochromatosis, thalassaemia major and in animal models of iron overload. An additional finding was the presence of aluminium accumulation in siderosomes of different cells. In liver biopsy samples from human Wilson's disease and from rats with an inherited disorder causing copper toxicosis, copper-containing compounds were identified and localized, and their relative concentration was estimated by LAMMA. The present study showed that LAMMA is a valuable technique for the localization and estimation of relative abundance of trace elements in various tissues containing excessive amounts of metals.     

Differential scaling within an insect compound eye

Environmental and genetic influences cause individuals of a species to differ in size. As they do so, organ size and shape are scaled to available resources whilst maintaining function. The scaling of entire organs has been investigated extensively but scaling within organs remains poorly understood. By making use of the structure of the insect compound eye, we show that different regions of an organ can respond differentially to changes in body size. Wood ant (Formica rufa) compound eyes contain facets of different diameters in different regions. When the animal body size changes, lens diameters from different regions can increase or decrease in size either at the same rate (a ‘grade’ shift) or at different rates (a ‘slope’ shift). These options are not mutually exclusive, and we demonstrate that both types of scaling apply to different regions of the same eye. This demonstrates that different regions within a single organ can use different rules to govern their scaling, responding differently to their developmental environment. Thus, the control of scaling is more nuanced than previously appreciated, diverse responses occurring even among homologous cells within a single organ. Such fine control provides a rich substrate for the diversification of organ morphology.     

Red Cell Membrane Permeability Deduced from Bulk Diffusion Coefficients

The permeability coefficients of dog red cell membrane to tritiated water and to a series of[¹⁴C]amides have been deduced from bulk diffusion measurements through a "tissue" composed of packed red cells. Red cells were packed by centrifugation inside polyethylene tubing. The red cell column was pulsed at one end with radiolabeled solute and diffusion was allowed to proceed for several hours. The distribution of radioactivity along the red cell column was measured by sequential slicing and counting, and the diffusion coefficient was determined by a simple plotting technique, assuming a one-dimensional diffusional model. In order to derive the red cell membrane permeability coefficient from the bulk diffusion coefficient, the red cells were assumed to be packed in a regular manner approximating closely spaced parallelopipeds. The local steady-state diffusional flux was idealized as a one-dimensional intracellular pathway in parallel with a one-dimensional extracellular pathway with solute exchange occurring within the series pathway and between the pathways. The diffusion coefficients in the intracellular and extracellular pathways were estimated from bulk diffusion measurements through concentrated hemoglobin solutions and plasma, respectively; while the volume of the extracellular pathway was determined using radiolabeled sucrose. The membrane permeability coefficients were in satisfactory agreement with the data of Sha'afi, R. I., C. M. Gary-Bobo, and A. K. Solomon (1971. J. Gen. Physiol. 58:238) obtained by a rapid-reaction technique. The method is simple and particularly well suited for rapidly permeating solutes.     

Reduced nicotinamide-adenine-dinucleotide-pyrophosphorylase: A novel enzyme in seeds

An enzyme which splits reduced NAD has been partially purified from pea (Pisum sativum, Kelvedon Wonder) seeds. The activity requires orthophosphate and the products are ADP and probably NMN (dihydro NMN?). The enzyme splits the NADH₂ at the pyrophosphate bond and incorporates the phosphate into the AMP residue. NAD, NADP or NADPH₂ could not replace NADH₂. The enzyme is unstable during storage, is activated by Mg²⁺ and by Mn²⁺, and inhibited by Ca²⁺. K⁺, Li⁺ and NH₄⁺ have no effect. The possible role of this enzyme in the synthesis of ATP in seeds at the early stage of germination is discussed.     

A possible ribosomal-directed regulatory system in Euglena gracilis. Chlorophyll synthesis

Cycloheximide at concentrations of 0.1-100mum stimulated chlorophyll synthesis when dark-grown cells of Euglena were illuminated. Chloramphenicol (1-4mm) inhibited chlorophyll synthesis. The effect of cycloheximide on the incorporation of [(14)C]leucine into material insoluble in trichloroacetic acid, and its failure to affect the incorporation of [(32)P]orthophosphate into such material in short incubations, are interpreted as evidence that cycloheximide specifically inhibits protein synthesis by 80S ribosomes. Since the inhibitory effect of chloramphenicol on chlorophyll synthesis is counteracted by the presence of cycloheximide, it is suggested that chlorophyll synthesis is subject to control by a cytoplasmic repressor synthesized on 80S ribosomes, and to a de-repressor synthesized on 70S ribosomes.     

Local Blood Flow in Human Leg Muscle Measured by a Transient Response Thermoelectric Method

The initial transient response of a Gibbs type thermoelectric probe embedded in human resting leg muscle was used for absolute quantitative measurement of local blood flow per unit tissue volume (local perfusion). The probe consisted of two thermistor-containing needles, one of which was heated by a constant electrical power input. The temperatures of both thermistors were recorded continuously on a two-channel, fast-response recorder. Upon sudden occlusion of the blood flow to the leg, each temperature vs. time record exhibited a change of slope. The change in slope of the temperature difference, divided by the temperature difference, (degrees/minute degree) was identified with the local perfusion (milliliters/minute milliliter) existing just before occlusion. The local perfusions determined agreed in range and mean with literature values of average perfusion by venous occlusion plethysmography. The nature of the local blood flow measured by the present method is discussed relative to that by other methods.