Exchange between inorganic phosphate and adenosine triphosphate in (Na+,K+)-ATPase

(Na⁺,K⁺)-ATPase is able to catalyze a continuous ATP?P_i exchange in the presence of Na⁺ and in the absence of a transmembrane ionic gradient. At pH 7.6 the Na⁺ concentration required for half-maximal activity is 85 mM and at pH 5.1 it is 340 mM. In the presence of optimal Na⁺ concentration, the rate of exchange is maximal at pH 6.0 and varies with ADP and P_i concentration in the assay medium. ATP?P_i exchange is inhibited by K⁺ and by ouabain.     

Light-, pH- and uncoupler-dependent association of chloride with chloroplast thylakoids

Studies of the association of Cl^? with Photosystem (PS) II in CF₁-containing thylakoid membranes revealed that photosynthetically active Cl^? is retained in a Cl^?-free medium unless it is sufficiently alkaline, uncoupling conditions are established and light is excluded. After treatment under such conditions, electron transport from water became dependent on added Cl^? under all conditions. Quantitative measurements of ³⁶Cl^? retention in the light revealed that there were about five Cl^? anions present in Cl^?-sufficient chloroplasts per PS II reaction center, and one-fourth of that in Cl^?-deficient samples. Uncouplers representing three different types of uncoupling mechanism were found to be effective mediators of Cl^? release from thylakoids. Since the ability to collapse a proton gradient probably is the only property shared by all the tested uncouplers, a proton gradient may be involved in the retention of Cl^?. As uncoupler-mediated Cl^? release did not depend on preillumination of our samples, a long-lived proton gradient must exist in dark-adapted chloroplasts which may not span the whole thickness of the thylakoid membrane. It is postulated that the Cl^? active in PS II reactions resides in a special membrane domain from which protons slowly equilibrate with those in the bulk solutions. Cl^? is thought to be released to the bulk phases only when the pH of the membrane domain is raised above a certain threshold by the action of uncouplers. This domain may be identical to the intramembranous compartment which has been postulated to be associated with PS II (Prochaska, L.J. and Dilley, R.A., (1978) Front. Biol. Res. Energ. 1, 265–274).     

Na+/solute symport in membrane vesicles from Bacillus alcalophilus

The characteristics of α-aminoisobutyric acid translocation were examined in membrane vesicles from obligately alkalophilic Bacillus alcalophilus and its non-alkalophilic mutant derivative, KM23. Vesicles from both strains exhibited α-aminoisobutyric acid uptake upon energization with ascorbate and N,N,N′,N′-tetramethyl-p-phenylenediamine. The presence of Na⁺ caused a pronounced reduction in the Km for α-aminoisobutyric acid in wild-type but not KM23 vesicles; the maximum velocity (V) was unaffected in vesicles from both strains. Passive efflux and exchange of α-aminoisobutyric acid from wild-type vesicles were Na⁺-dependent and occurred at comparable rates (with efflux slightly faster than exchange). This latter observation suggests that the return of the unloaded carrier to the inner surface is not rate-limiting for efflux. The rates of α-aminoisobutyric acid efflux and exchange were also comparable in KM23 vesicles, but were Na⁺-independent. Furthermore, in vesicles from the two strains, both efflux and exchange were inhibited by generation of a transmembrane electrochemical gradient of protons, outside positive. This suggests that the ternary complex between solute, carrier, and coupling ion bears a positive charge in both strains even though the coupling ion is changed. Evidence from experiments with an alkalophilic strain that was deficient in l-methionine transport indicated that the porters, i.e., the solute-translocating elements, used by non-alkalophilic mutants are not genetically distinct from those used by the alkalophilic parent; that is, the change in coupling ion cannot be explained by the expression of a completely new set of Na⁺-independent, H⁺-coupled porters upon mutation of B. alcalophilus to non-alkalophily.     

Energy thresholds for ATP synthesis in chloroplasts

We have investigated the ATP synthesis associated with acid-base transitions in chloroplast lamellae under conditions which allow simultaneous control of the thermodynamic variables, ΔpH, membrane potential and ΔG_ATP. These variables have been directly imposed rather than simply inferred. Since the initiation of labeled P_i incorporation seems to measure accurately the initiation of net ATP synthesis, the following conclusions can be drawn: (1) The proton-motive force which is just sufficient for ATP synthesis provides almost exactly the required energy for ΔG_ATP if the efflux of three H⁺ is required for each ATP molecule formed. (2) The membrane potential and the ΔpH contribute to the proton-motive force in a precisely additive way. Thus, the threshold can be reached or exceeded by a ΔpH in the absence of a membrane potential, by a membrane potential in the absence of a ΔpH, or by any combination of membrane potential and ΔpH. With a large enough membrane potential, ATP synthesis occurs even against a small inverse ΔpH. In each instance the combined ΔpH and membrane potential necessary for initiation of ATP synthesis represent the same threshold proton-motive force.     

Isolation and assay of corn root membrane vesicles with reduced proton permeability

Conditions promoting the formation of sealed membrane vesicles from corn roots with reduced proton permeability were examined using the probe 9-aminoacridine as a rapid indicator of pH gradient formation and dissipation. Plasma membrane vesicles isolated by differential and density gradient centrifugation were leaky to protons and rapidly equilibrated when exposed to artificially imposed pH gradients. The leaky plasma membrane vesicles showed reduced proton permeability when incubated with calcium or with excess phospholipids. However, these vesicles were unable to form ATP-induced pH gradients. Sealed vesicles isolated by discontinuous Ficoll gradient centrifugation of a microsomal fraction displayed reduced proton permeability and were osmotically active. In contrast to purified plasma membrane vesicles, the microsomal-derived vesicles were more suitable for studies of active proton transport.     

Ion pathways in renal brush border membranes

The absorbance change of the weak base dye probe, Acridine orange, was used to monitor alterations of pH gradients across renal brush border membrane vesicles. The presence of Na⁺/H⁺ or Li⁺/H⁺ exchange was demonstrated by diluting Na₂SO₄ or Li₂SO₄ loaded vesicles into Na⁺- or Li⁺-free solutions, which caused dye uptake. About 20% of the uptake was abolished by lipid permeable cations such as valinomycin-K⁺ or tetraphenylphosphonium, indicating perhaps the presence of a finite Na⁺ conductance smaller than electroneutral Na⁺/H⁺ exchange. The protonophore tetrachlorosalicylanilide raised the rate of dye uptake under these conditions, hence the presence of an Na⁺ conductance greater than the H⁺ conductance was suggested. K⁺ gradients also induced changes of pH, at about 10% of the Na⁺ or Li⁺ rate. Partial inhibition (21%) was seen with 0.1 mM amiloride indicating that K⁺ was a low affinity substrate for the Na⁺/H⁺ exchange. Acceleration both by tetrachlorosalicylanilide (2-fold) and valinomycin (4-fold) suggested the presence of 2 classes of vesicles, those with high and those with low K⁺ conductance. The larger magnitude of the valinomycin dependent signal suggested that 75% of the vesicles had a low K⁺ conductance. Inward Cl^? gradients also induced acidification, partially inhibited by the presence of tetraphenylphosphonium, and accelerated by tetrachlorosalicylanilide. Thus both a Cl^? conductance greater than the H⁺ conductance and a Cl^?/OH^? exchange were present. The rate of Na⁺/H⁺ exchange was amiloride sensitive with a pH optimum of 6.5 and an apparent K_m for Na⁺ or Li⁺ of about 10 mM and an E_A of 14.3 kcal per mol. A 61-fold Na₂SO₄ gradient resulted in a pH gradient of 1.64 units which increased to 1.8 with gramicidin. An equivalent NaCl gradient gave a much lower ΔpH even in the presence of gramicidin showing that the H⁺ and Cl^? pathways could alter the effects of the Na⁺/H⁺ exchange.     

长爪沙鼠与黑线仓鼠的温度选择比较

本文使用自制的陆生动物温度选择仪,对长爪沙鼠和黑线仓鼠的温度选择进行了比较,结果表明,长爪沙鼠的选择温度(29.06±0.62℃)较黑线仓鼠(26.65±0.64℃)高。这种差异可能与两种鼠的栖息环境及昼夜节律的不同有关。     

Opto-thermal technologies for microscopic analysis of cellular temperature-sensing systems

Could enzymatic activities and their cooperative functions act as cellular temperature-sensing systems? This review introduces recent opto-thermal technologies for microscopic analyses of various types of cellular temperature-sensing system. Optical microheating technologies have been developed for local and rapid temperature manipulations at the cellular level. Advanced luminescent thermometers visualize the dynamics of cellular local temperature in space and time during microheating. An optical heater and thermometer can be combined into one smart nanomaterial that demonstrates hybrid function. These technologies have revealed a variety of cellular responses to spatial and temporal changes in temperature. Spatial temperature gradients cause asymmetric deformations during mitosis and neurite outgrowth. Rapid changes in temperature causes imbalance of intracellular Ca²⁺ homeostasis and membrane potential. Among those responses, heat-induced muscle contractions are highlighted. It is also demonstrated that the short-term heating hyperactivates molecular motors to exceed their maximal activities at optimal temperatures. We discuss future prospects for opto-thermal manipulation of cellular functions and contributions to obtain a deeper understanding of the mechanisms of cellular temperature-sensing systems.     

Latitudinal gradients in sexual dimorphism: Alternative hypotheses for variation in male traits

Biological patterns across latitudinal gradients elucidate a number of striking natural clines from which numerous processes can be further explored. The trade‐off between reproduction and somatic maintenance and growth represents a suite of life‐history traits with variable energy allocation and potential latitudinal patterns. Specifically, male sexually dimorphic traits in female choice systems represent one such reproductive investment constrained by resource acquisition and subsequent allocation. Latitudinal variation in sexual dimorphism has been suggested although the relationship between dimorphic traits and latitude are conflicting. Here, we test alternative hypotheses regarding this pattern using two broadly distributed vertebrates exhibiting sexually dimorphic traits. We hypothesized that the exaggeration of dimorphic traits correlates with latitude, with males having exaggerated sexually dimorphic traits at either higher or lower latitudes. Results indicate that male sexually dimorphic traits are exaggerated at lower latitudes while relative gonopodium size in Poecilia latipinna was larger at higher latitudes. This pattern may be a result of lower latitude populations experiencing greater population densities and longer access to resources that could manifest in females more intensively selecting for higher quality males in lower latitudes. Experimental work should address this pattern and investigate mechanistic processes.