bluuebunny/crossref_metadata_2025_split huggingface dataset:
Amino Acid Uptake and Metabolism by Embryos of the Blenny Zoarces Viviparus
Authors: Korsgaard Bodil 
Published: April 2021

ABSTRACT
The ability of blenny Zoarces viviparus (L.) embryos in early and late development to assimilate and metabolize ambient L-alanine was investigated in vitro and in vivo by means of autoradiographic and radiochemical methods. Autoradiograms showed that after 24 h of exposure to L-[14C]alanine, label was distributed in the tissues of the embryos.
Uptake rates for l4C-labelled L-alanine in vitro were estimated by measuring the disappearance of radioactivity from the medium. Net uptake rates were measured by high performance liquid chromatography of samples taken simultaneously from the medium. Uptake rates, based on uptake of the tracer (0.60 μmol g−1 h−1), were similar to net uptake rates (0.54 μmol g−1 h−1) in embryos in late development in the in vitro incubations in 60 μmol l−1 alanine. In vivo, the injected tracer was completely cleared from the ovarian fluid over 24h. After intraovarian and in vitro incubation of the embryos with labelled alanine, there was evidence for both catabolic and anabolic metabolism of the amino acid by production of l4CO2 and by incorporation of radioactivity into molecules insoluble in trichloroacetic acid, respectively.
The data provide evidence for uptake and metabolism of amino acids by embryos in vitro and in vivo. An increase in the capacity for uptake and metabolism of L-alanine may occur during development of the embryos in the ovary.
Influence of Haemoglobin Conformation, Nitrite and Eicosanoids on K+ Transport Across the Carp Red Blood Cell Membrane
Authors: Jensen Frank B. 
Published: April 2021

ABSTRACT
The regulation of K+ transport across the red blood cell (RBC) membrane by haemoglobin (Hb) conformation was studied in carp, and the K+ transport mechanisms were identified. When a large proportion of Hb in the R quaternary structure was secured by oxygenation of blood at pH 8.14, a net RBC K+ efflux was induced, which was accompanied by RBC shrinkage. This K+ efflux was resistant to ouabain and inhibited by furosemide and DIDS and by substitution of NO3− for Cl−, showing it to result from a K+/C1− cotransport mechanism. Deoxygenation of the RBCs (Hb in T structure) eliminated the Cl−-dependent K+ efflux and resulted in a net K+ uptake via the Na+/K+ pump. These changes were fully reversible. Nitrite-induced methaemoglobin formation in deoxygenated blood, which converts a large fraction of the T structure Hb into an R-like conformation, shifted the K+ uptake to a Cl−-dependent K+ efflux similar to that seen in oxygenated cells. When the allosteric equilibrium between the R and T structures of Hb was gradually shifted towards the T state by decreases in pH, the Cl−-dependent K+ efflux from oxygenated cells decreased. At pH 7.52, where the Root effect caused a potent stabilisation of the T state, the K+ efflux was reversed to a net K+ uptake. A similar change was induced in methaemoglobin-containing deoxygenated blood, since low pH also favours a T-like conformation of metHb. The variable K+ fluxes could not be related to changes in membrane potential or pH but were always directly related to the experimental modulation of the relative proportions of R-and T-structure Hb. It is proposed that Hb conformation governs K+ movements via a different binding of T and R structures to integral membrane proteins, and that a large fraction of R-structure Hb triggers the Cl−-dependent K+ efflux mechanism. Application of inhibitors and a substrate of prostaglandin and leukotriene synthesis did not influence the K+ efflux from oxygenated erythrocytes. However, a fraction of the K+ efflux from nitrite-treated deoxygenated cells was inhibited by nordihydroguaiaretic acid, suggesting that a slightly larger K+ efflux from these RBCs than from oxygenated RBCs was related to leukotriene production caused by nitrite entry. A much larger influx of nitrite to deoxygenated than to oxygenated RBCs was positively correlated with the distribution ratio of H+ and the membrane potential, supporting the view that nitrite primarily enters the cells via conductive transport. The physiological implications of the results are discussed.
Modulation of Aplysia Californica Siphon Sensory Neurons by Conopressin G
Authors: Martínez-Padrón Manuel , Edstrom John , Wickham Michael , Lukowiak Ken 
Published: April 2021

ABSTRACT
Conopressin G, a molluscan vasopressin-like peptide, when superfused over the abdominal ganglion suppressed gill withdrawal reflex behavior patterns. The effects of conopressin G on Aplysia californica central sensory neurons and on the sensory neuron to motor neuron synapse were inconsistent with its behavioral effects. That is, superfusion of the peptide facilitated synaptic transmission at this synapse and reversed low-frequency homosynaptic depression. Further, conopressin G potentiated frequency-dependent spike broadening, reduced spike threshold and reduced accommodation. A voltage-dependent outward K+ current was suppressed by the peptide. This current was also suppressed by Co2+ and Ba2+ and was relatively resistant to tetraethylammonium and 4-aminopyridine. The effects produced by conopressin G on the sensory neurons were not observed when Ca2+ was removed from the saline, when a low-Ca2+, high-Mg2+ saline was used or when other procedures that impair synaptic transmission were used. These results suggest that the effects of conopressin G were mediated by a polysynaptic pathway acting on the sensory neurons.
Physiology of V-ATPases
Authors: Harvey William R. 
Published: April 2021

ABSTRACT
Protons migrate much faster than other ions through water, ice and water-lined membrane channels because they participate in hydrogen bonding and H+H2O exchange. Similarly, hydrogen bonding enables protons with amino, carbonyl, phosphoryl and sulfonyl residues to influence critically the charge, conformation and stability of proteins. Therefore, it is not surprising that regulation of proton concentration, or pH, is an essential requirement in biological systems. It is no surprise either that enzymes which regulate proton concentration (i.e. proton pumps) should have evolved or that evolution should have used these enzymes further, for energization of biological membranes. At present there appear to be three classes of ATP-hydrolyzing proton pumps, or H+-ATPases, which were dubbed P-ATPases, F-ATPases and V-ATPases, by Pederson and Carafoli (1987). H+-translocating P-ATPases, as well as the Na+/K+-ATPase of plasma membranes and the Ca2+-ATPase of sarcoplasmic reticulum, form phosphoaspartyl intermediates and are inhibited by the phosphate analogue orthovanadate. F-ATPases are the proton-translocating ATP synthases of mitochondria, chloroplasts and bacterial plasma membranes and are inhibited by azide.
The plant vacuole
Authors: Taiz Lincoln 
Published: April 2021

ABSTRACT
Plant cells are unique in containing large acidic vacuoles which occupy most of the cell volume. The vacuolar H+-ATPase (V-ATPase) is the enzyme responsible for acidifying the central vacuole, although it is also present on Golgi and coated vesicles. Many secondary transport processes are driven by the proton-motive force generated by the V-ATPase, including reactions required for osmoregulation, homeostasis, storage, plant defense and many other functions. However, a second proton pump, the V-PPase, serves as a potential back-up system and may, in addition, pump potassium. The plant V-ATPase is structurally similar to other eukaryotic V-ATPases and its subunits appear to be encoded by small multigene families. These multigene families may play important roles in the regulation of gene expression and in the sorting of V-ATPase isoforms to different organelles.
Vacuolar-type H+-translocating ATPases IN plant endomembranes: subunit organization and multigene families
Authors: Sze Heven , Ward John M. , Lai Shoupeng , Perera Imara 
Published: April 2021

ABSTRACT
Acidification of endomembrane compartments by the vacuolar-type H+-translocating ATPase (V-ATPase) is vital to the growth and development of plants. The V-ATPase purified from oat roots is a large complex of 650×10Mr that contains 10 different subunits of 70, 60,44,42, 36, 32, 29, 16, 13 and 12 × 103Mr. This set of ten polypeptides is sufficient to couple ATP hydrolysis to proton pumping after reconstitution of the ATPase into liposomes. Unlike some animal V-ATPases, the purified and reconstituted V-ATPase from oat is directly stimulated by Cl−. The peripheral complex of the ATPase includes the nucleotide-binding subunits of 70 and 60 × 103Mr and polypeptides of 44, 42, 36 and 29 × 103Mr. Six copies of the 16 × 103Mr proteolipid together with three other polypeptides are thought to make up the integral sector that forms the H+-conducting pathway. Release of the peripheral complex from the native membrane completely inactivates the pump; however, the peripheral subunits can be reassembled with the membrane sector to form a functional H+ pump.
Comparison of V-ATPases from several plants indicates considerable variations in subunit composition. Hence, several forms of the V-ATPase may exist among, and probably within, plant species. At least four distinct cDNAs encode the 16 × 103Mr proteolipid subunit in oat. Multiple genes could encode different subtypes of the H+ pump that are regulated by the developmental stage and physiological function specific to the cell or tissue type.
Evolution and isoforms of V-ATPase subunits
Authors: Gogarten J. Peter , Starke Thomas , Kibak Henrik , Fishmann Jenny , Taiz Lincoln 
Published: April 2021

ABSTRACT
The structure of V- and F-ATPases/ATP synthases is remarkably conserved throughout evolution. Sequence analyses show that the V- and F-ATPases evolved from the same enzyme that was already present in the last common ancestor of all known extant life forms. The catalytic and non-catalytic subunits found in the dissociable head groups of both V-ATPases and F-ATPases are paralogous subunits, i.e. these two types of subunits evolved from a common ancestral gene. The gene duplication giving rise to these two genes (i.e. those encoding the catalytic and non-catalytic subunits) pre-dates the time of the last common ancestor. Similarities between the V- and F-ATPase subunits and an ATPase-like protein that is implicated in flagellar assembly are evaluated with regard to the early evolution of ATPases. Mapping of gene duplication events that occurred in the evolution of the proteolipid, the non-catalytic and the catalytic subunits onto the tree of life leads to a prediction of the likely quaternary structure of the encoded ATPases. The phylogenetic implications of V-ATPases found in eubacteria are discussed.
Different V-ATPase isoforms have been detected in some higher eukaryotes, whereas others were shown to have only a single gene encoding the catalytic V-ATPase subunit. These data are analyzed with respect to the possible function of the different isoforms (tissue-specific, organelle-specific). The point in evolution at which the different isoforms arose is mapped by phylogenetic analysis.
Structure and function of V-ATPases in endocytic and secretory organelles
Authors: Nelson Nathan 
Published: April 2021

ABSTRACT
Chromaffin granules and clathrin-coated vesicles are major sources for V-ATPases of mammalian cells. Studies of these organelles have helped us to understand the structure and function of the enzyme. It was shown that V-ATPases are composed of distinct catalytic and membrane sectors containing several subunits. The subunit stoichiometry was determined to be 3A, 3B, 1C, 1D, 1E, 6c (proteolipids), 1Acl 15 and ?Ac39. Additional subunits are likely to be discovered. Resolution and reconstitution of the enzyme revealed that the catalytic and membrane sectors are interdependent for their partial activity. The catalytic sector has no ATPase activity when detached from the membrane sector, and the membrane sector when depleted of the catalytic sector does not conduct protons. The mechanistic significance of these properties is discussed.
The vacuolar H+-ATPase – one of the most fundamental ion pumps in nature
Authors: Nelson Nathan 
Published: April 2021

ABSTRACTAn electrochemical gradient of protons (PMF) is a universal high-energy intermediate in biological systems. Two related families of proton pumps, denoted F-and V-ATPases, are among the principal generators of a PMF from ATP and can form ATP at the expense of a PMF. The enzymes of these two families share a similar structure and subunit composition; some subunits in the two families evolved from common ancestors. Other subunits having no common ancestry were added independently to the various enzymes and defined the two separate families. The general mechanism for the proton pumping activity is similar in the two families. However, whereas F-ATPases can act in both proton pumping and ATP formation, the V-ATPases of eukaryotes function exclusively as ATP-dependent proton pumps. The catalytic and membrane sectors of F-ATPases and archaebacterial V-ATPases can separately catalyze their specific partial activities of ATPase and proton conduction. The catalytic and membrane sectors of the eukaryotic V-ATPases cannot act separately. This property is correlated with the presence of a large proteolipid that traverses the membrane four times. The gene duplication of the smaller proteolipid in the formation of the large proteolipid was one of the most important events in the evolution of the V-ATPases of eukaryotic cells.
Driving Forces and Pathways For H+ and K+ Transport in Insect Midgut Goblet Cells
Authors: Moffett David F. , Koch Alan 
Published: April 2021

ABSTRACT
In the midgut of larval lepidopteran insects, goblet cells are believed to secrete K+; the proposed mechanism involves an electrogenic K+/nH+ (n&gt;l) antiporter coupled to primary active transport of H+ by a vacuolar-type ATPase. Goblet cells have a prominent apical cavity isolated from the gut lumen by a valve-like structure.
Using H+- and K+-selective microelectrodes, we showed that electrochemical gradients of H+ and K+ across the apical membrane and valve are consistent with active secretion of both ions into the cavity and that the transapical H+ electrochemical gradient, but not the transapical pH gradient, is competent to drive K+ secretion by a K+/nH+ antiporter.
We used 10 mmol l−1 tétramethylammonium ion (TMA+) as a marker for the ability of small cations to pass from the gut lumen through the valve to the goblet cavity, exploiting the high TMA+ sensitivity of ‘K+-sensitive’ microelectrodes. These studies showed that more than half of the cavities were inaccessible to TMA+. For those cavities that were accessible to TMA+, both entry and exit rates were too slow to be consistent with direct entry through the valves. One or more mixing compartments appear to lie between the lumen bathing solution and the goblet cavity. The lateral intercellular spaces and goblet cell cytoplasm are the most likely compartments. The results are not consistent with free diffusion of ions in a macroscopic valve passage; mechanisms that would allow K+ secreted into the goblet cavity to exit to the gut lumen, while preventing H+ from exiting, remain unclear.
Halobacterial A-ATP synthase in relation to V-ATPase
Authors: Ihara Kunio , Abe Tadahiro , Sugimura Ken-Ichiro , Mukohata Yasuo 
Published: April 2021

ABSTRACT
The head piece separated from the A-ATP synthase of Halobacterium halobium hydrolyses ATP. This A1-ATPase is inhibited by nitrate but not by other chaotropic anions. The nitrate inhibition is noncompetitive with respect to ATP, reversible, and partially protected by chloride. In contrast, ATP synthase in situ (A1Ao-ATPase) is not inhibited by nitrate but apparently is inhibited by stronger chaotropic reagents, such as thiocyanate and trichloroacetate, which make the vesicle membrane permeable to protons. The mode of action of nitrate and chaotropic anions seems to differentiate A-ATPases from V-ATPases.
Other strains of Halobacterium, Haloferax, Haloarcula, Halococcus and Natronobacterium, contain at least two polypeptides immunochemically similar to the two major subunits, a (86× 103Mr on SDS-PAGE) and β (64×103Mr), of the A-ATPase of Halobacterium halobium. When solubilized, membrane vesicles of these halobacteria hydrolyse ATP. Their ATPases are commonly sensitive to nitrate. They require high concentrations of the supporting salt but depend differently on chloride or sulfate/sulfite. The A-ATPases of Halobacteriaceae appear to diverge with respect to salt preference.
Molecular genetics of the yeast vacuolar H+-ATPase
Authors: Anraku Yasuhiro , Hirata Ryogo , Wada Yoh , Ohya Yoshikazu 
Published: April 2021

ABSTRACT
The yeast vacuolar proton-translocating ATPase was discovered in 1981 as the first member of the V-ATPases, which are now known to be ubiquitously distributed in eukaryotic vacuo-lysosomal organelles and archaebacteria. Nine VMA genes that are indispensable for expression of vacuolar ATPase activity have been identified in the yeast Saccharomyces cerevisiae. VMA1, VMA2, VMA3, VMA5 and VMA6 were cloned and characterized on the basis of partial amino acid sequences determined with the purified subunits. Genetic and biochemical studies of the yeast Pet–cls mutants have demonstrated that they are related to vma defects. Based on this evidence, VMA11 (CLS9), VMA 12 (CLS10) and VMA 13 (CLS11) were isolated from a yeast genomic DNA library by complementation of the vmal 1, vma!2 and vma!3 mutations, respectively. This article summarizes currently available information on the VMA genes and the molecular biological functions of the VMA gene products.
Comparative Rheology of Human and Trout Red Blood Cells
Authors: Nash Gerard B. , Egginton Stuart 
Published: April 2021

ABSTRACT
We have studied the comparative rheology of individual red blood cells from humans and rainbow trout (Oncorhynchus mykiss) at their natural body temperatures. Trout red blood cells were large ellipsoids (about 16 µmX11.5 µmX2.5 µm) with a mean volume of 250 fl, a surface area of approximately 350 µm2 and an elongated nucleus of about 9 µmX5 µm. Although much larger than human red cells (diameter 8 µm, V=92 fl, A= 136 µm2), both theoretical calculation and experimental aspiration into micropipettes indicated that the limiting size of a cylindrical vessel that both types of cell could enter was approximately 3 µm. Nevertheless, individual trout red cells had much longer transit times through 5 µm filter pores and were much slower to enter 3–4 µm diameter micropipettes. Interestingly, the relative deformability of the trout cells depended on the pore size and applied pressure, with entry times for trout and human cells converging as pipette diameter increased. The relatively poor overall cellular deformability of the trout cells reflected their membrane rigidity (shear elastic modulus 4–5 times higher than that of human membrane), as well as their large size and the presence of a prominent nucleus. Capillary diameters in trout muscle are similar to those in the human microcirculation (about 3 µm), while systemic driving pressures are much lower. Therefore, either red cell deformability is a less critical circulatory parameter than has previously been thought, or the apparently disadvantageous blood rheology of trout is adequate because of the lower demand for tissue perfusion.
Temperature, Muscle Power Output and Limitations on Burst Locomotor Performance of the Lizard Dipsosaurus Dorsalis
Authors: Swoap Steven J. , Johnson Timothy P. , Josephson Robert K. , Bennett Albert F. 
Published: April 2021

ABSTRACT
The mechanical power output of fast-twitch fibres from the iliofibularis of the lizard Dipsosaurus dorsalis was measured over a broad body temperature range using the oscillatory work-loop technique. The optimal cycling frequency, that frequency at which mechanical power output is maximal, increases with temperature from 3.3Hz at 15°C to 20.1Hz at 42°C. Maximum power output increases with temperature, from 20 W kg-1 at 15°C to 154 W kg-1 at 42°C, the largest power output yet measured using the work-loop technique. At low temperatures (15°C and 22°C), stride frequency during burst running is nearly identical to the optimal cycling frequency for in vitro power output, suggesting that maximum power output may limit hindlimb cycle frequency in vivo. However, at higher temperatures (35°C and 42°C), the optimal cycling frequency of the isolated muscle is significantly higher than the burst stride frequency, demonstrating that contractile events no longer limit hindlimb cycle frequency. At higher temperatures, it is thus unlikely that the fast-twitch fibres of this muscle in vivo attain their potential for maximum power output.
Unsteady Aerodynamic Performance of Model Wings at Low Reynolds Numbers
Authors: Dickinson Michael H. , Götz Karl G. 
Published: April 2021

ABSTRACT
The synthesis of a comprehensive theory of force production in insect flight is hindered in part by the lack of precise knowledge of unsteady forces produced by wings. Data are especially sparse in the intermediate Reynolds number regime (10&lt;Re&lt;1000) appropriate for the flight of small insects. This paper attempts to fill this deficit by quantifying the time-dependence of aerodynamic forces for a simple yet important motion, rapid acceleration from rest to a constant velocity at a fixed angle of attack. The study couples the measurement of lift and drag on a two-dimensional model with simultaneous flow visualization. The results of these experiments are summarized below. At angles of attack below 13.5°, there was virtually no evidence of a delay in the generation of lift, in contrast to similar studies made at higher Reynolds numbers.At angles of attack above 13.5°, impulsive movement resulted in the production of a leading edge vortex that stayed attached to the wing for the first 2 chord lengths of travel, resulting in an 80% increase in lift compared to the performance measured 5 chord lengths later. It is argued that this increase is due to the process of detached vortex lift, analogous to the method of force production in delta-wing aircraft.As the initial leading edge vortex is shed from the wing, a second vortex of opposite vorticity develops from the trailing edge of the wing, correlating with a decrease in lift production. This pattern of alternating leading and trailing edge vortices generates a von Karman street, which is stable for at least 7.5 chord lengths of travel.Throughout the first 7.5 chords of travel the model wing exhibits a broad lift plateau at angles of attack up to 54°, which is not significantly altered by the addition of wing camber or surface projections.Taken together, these results indicate how the unsteady process of vortex generation at large angles of attack might contribute to the production of aerodynamic forces in insect flight. Because the fly wing typically moves only 2–4 chord lengths each half-stroke, the complex dynamic behavior of impulsively started wing profiles is more appropriate for models of insect flight than are steady-state approximations.