A respiration-dependent primary sodium extrusion system functioning at alkaline pH in the marine bacterium Vibrioalginolyticus

The membrane potential generated at pH 8.5 by K⁺-depleted and Na⁺-loaded $\text{Vibrio}\text{alginolyticus}$ is not collapsed by proton conductors which, instead, induce the accumulation of protons in equilibrium with the membrane potential. The generation of such a membrane potential and the accumulation of protons are specific to Na⁺-loaded cells at alkaline pH and are dependent on respiration. Extrusion of Na⁺ at pH 8.5 occurs in the presence of proton conductors unless respiration is inhibited while it is abolished by proton conductors at acidic pH. The uptake of α-aminoisobutyric acid, which is driven by the Na⁺-electrochemical gradient, is observed even in the presence of proton conductors at pH 8.5 but not at acidic pH. We conclude that a respiration-dependent primary electrogenic Na⁺ extrusion system is functioning at alkaline pH to generate the proton conductor-insensitive membrane potential and Na⁺ chemical gradient.     

The photosynthetic electron transfer chain of Chromatium vinosum chromatophores flash-induced cytochrome b reduction

Reduction of a cytochrome b following excitation by a single, short, near-saturating light flash has been demonstrated in Chromatium vinosum chromatophores. The extent of reduction is increased by addition of antimycin. The cytochrome has an α-band maximum at 562 nm in the presence of antimycin.The cytochrome b reduction is most readily observed in the presence of antimycin at high redox potential when cytochrome c-555 is oxidised before excitation. Under these conditions the half-time for reduction is about 20 ms, and the extent is about 0.5 mol of cytochrome b reduced per mol of reaction center oxidised. This extent of reduction is observed on the first flash-excitation from the dark-adapted state, and there was no indication that the reaction center quinone acceptor complex acted as a two-electron accumulating system. With cytochrome c-555 reduced before excitation, the extent of cytochrome b reduction is approximately halved. The factors which result in substoichiometric cytochrome b reduction are not yet understood.Agents which appear to inhibit primary acceptor oxidation by the secondary acceptor (UHDBT, PHDBT, DDAQQ, HOQNO, o-phenanthroline), inhibit reduction of the cytochrome b. DBMIB inhibits cytochrome b reduction but does not appear to inhibit primary acceptor oxidation.These observations confirm that a cytochrome b receives electrons delivered from the primary acceptor complex, and indicate that the photoreduced cytochrome b is reoxidised via an antimycin-sensitive pathway.     

Genetic analysis of transpositions in the lac region of Escherichia coli

The lac region of Escherichia coli, carried on an F′ lacproB episome, was used as a target for the transposition of several transposable elements. Tn9 shows a preferential integration (by a factor of 50) into a region extending from the end of the Z gene through the Y gene. Throughout the remainder of the lacI, Z and Y genes one other short region, located in the middle of the I gene, is favored for integration. Within these favored regions many different integration points are evident. Inspection of the DNA sequence for the I and Y genes, and parts of the Z gene, shows a strong correlation between A + T richness and regions of preferential integration. Tn5 insertions follow a similar pattern, although with less preference; whereas Tn10 insertions (provided by T. J. Foster), also favor the Y gene and the end of Z, but are distributed among fewer integration points. Most of the Tn3 insertions into the episome are accompanied by a nearby or adjacent deletion.     

Ca2+ regulated modulator protein interacting agents: inhibition of Ca2+-Mg2+-ATPase of human erythrocyte ghost.

Agents such as N-(6-aminohexyl)-5-chloro-1-naphthalenesulfonamide (W-7), and its derivatives, chlorpromazine and amitriptyline that interact with calcium-regulated modulator protein were found to inhibit not only Ca²⁺ dependent cyclic nucleotide phosphodiesterase but also Ca²⁺-Mg²⁺-ATPase of human erythrocyte ghosts. I₅₀ values of modulator interacting agents for testis modulator-activated, brain modulator-activated and erythrocyte modulator-activated-ATPase are indistinguishable. However, I₅₀ of W-7 for troponin C-activated-ATPase is lower than that for modulator-activated ATPase. The specificity of these agents toward modulator-related enzyme reaction is also shown by the negative effect on modulator-unrelated enzyme system such as erythrocyte ghost protein kinase and Mg²⁺-ATPase. These agents provide a useful tool for elucidating the physiological role of modulator.     

Regulation of proton leakage from broken chloroplasts by CF0.

Measurements of proton translocation in CF₁-depleted, N, N′-dicyclohexylcarbodiimide-resealed broken chloroplasts were made under different light intensities. Kinetic analysis of the data shows that the outward leakage of accumulated protons through CF₀ is still dependent on light intensity with a first-order rate constant equal to mR₀, where R₀ is the initial rate of proton uptake which normally increases with light intensity and m is a characteristic constant which is independent of proton gradient and light intensity. Measurements of proton translocation in these modified chloroplasts cross-linked with glutaraldehyde under illumination and in the dark respectively suggest that the light-dependent proton leakage through CF₀ is regulated by conformation change in the membrane. It is proposed that the ovserved regulation of proton leakage through the CF₁.CF₀ complex in native chloroplasts is for optimizing the steady state synthesis of ATP under different light intensities.     

Thermoregulatory responses to temperature manipulation of the spinal cord in the marmot

Yellow-bellied marmots (M. flaviventris) acclimated to T_a = 20 °C were implanted with U-shaped polyethylene thermodes in the peridural space of the spinal cord. Decreasing the temperature of the cervical, thoracic, or lumbar areas of the cord increased heart rate, electromyographic activity, and oxygen consumption in the animals. These responses differed qualitatively from those elicited by heating the same cord areas, indicating specificity of the response to the temperature change.Increases in heat production were proportional to the amount of cooling of the cord. The thoracic area was found to be more thermosensitive than the lumbar area. No behavioral or physical thermoregulation was apparent when the spinal cord temperature was changed in these animals.In addition to the conclusion that regulation of spinal cord temperature may be important in the euthermic marmot, it was postulated that the temperature receptors located in the thoracic cord of the marmot may be important in maintaining shivering thermogenesis during arousal from hibernation.     

Hyaluronidase activity and hyaluronate content of the developing chick embryo heart.

Hyaluronidase activity and hyaluronate content were measured in the developing chick heart from embryonic day 3 through posthatching stages. High levels of both enzyme and substrate were found during the earliest stages examined. Hyaluronidase activity gradually declined to 63% of the initial (day 3) level by embryonic day 16. Enzyme activity decreased more sharply during the next 4 days to 30% of the initial level and remained constant through 2 weeks after hatching. Low levels of enzyme activity (about 10% initial levels) were still detectable in 10-week-old chicken hearts. The heart hyaluronidase is an endoglycosidase with an estimated molecular weight of 62,000, which degrades hyaluronate and, to a lesser extent, chondroitin sulfate at an acid pH optimum. Hyaluronate constituted approximately 50% of the total glycosaminoglycan content at embryonic day 5. Between embryonic days 5 and 12, the concentration of hyaluronate decreased to 25–30% of the initial level and remained constant thereafter. The level of other glycosaminoglycans decreased more gradually than hyaluronate and did not reach a constant level until hatching. This pattern of hyaluronidase activity and hyaluronate concentration presumably reflects the extensive tissue remodeling which transforms the developing heart from a thin-walled tube containing extensive regions of extracellular matrix to a compact, thick-walled myocardium having a limited extracellular compartment.     

The cryopreservation of mouse leukemic cells. I. Effects on drug resistance and the patterns of nucleic acid metabolism.

Cultured L1210 lymphocytic leukemic cells resistant to cytosine arabinoside or Cytoxan were frozen under different conditions for up to 5 months and transplanted into recipient mice. Biochemical determinations including DNA, total RNA and drug resistance suggested that the more rapid, less expensive method of freezing mouse leukemic cells enables good retention of each parameter. Examination of cellular and subcellular RNA fingerprints indicated several alterations in the localizations f certain subspecies of RNA. Nonetheless, all cells retained their overall viability and the capacity to induce leukemia in CDF₁ mice.