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Query: UMLS:C0027960 (mole)
 21,279 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Characteristics of cation permeation through voltage-dependent delayed rectifier K channels in squid giant axons were examined. Axial wire voltage-clamp measurements and internal perfusion were used to determine conductance and permeability properties. These K channels exhibit conductance saturation and decline with increases in symmetrical K+ concentrations to 3 M. They also produce ion- and concentration-dependent current-voltage shapes. K channel permeability ratios obtained with substitutions of internal Rb+ or NH+4 for K+ are higher than for external substitution of these ions. Furthermore, conductance and permeability ratios of NH+4 or Rb+ to K+ are functions of ion concentration. Conductance measurements also reveal the presence of an anomalous mole fraction effect for NH+4, Rb+, or Tl+ to K+. Finally, internal Cs+ blocks these K channels in a voltage-dependent manner, with relief of block by elevations in external K+ but not external NH+4 or Cs+. Energy profiles for K+, NH+4, Rb+, Tl+, and Cs+ incorporating three barriers and two ion-binding sites are fitted to the data. The profiles are asymmetric with respect to the center of the electric field, have different binding energies and electrical positions for each ion, and (for K+) exhibit concentration-dependent barrier positions.
J Gen Physiol 1987 Aug
PMID:Cation permeation through the voltage-dependent potassium channel in the squid axon. Characteristics and mechanisms. 244 3

Seasonal changes in testicular histology and steroidogenesis were investigated in the mole (Talpa europaea). Androgen synthesis was examined by incubating [4-14C]pregnenolone (P) and [4-14C]dehydroepiandrosterone (DHA) with testicular minces in a static incubation system. The metabolites formed were characterized by thin-layer chromatography. Morphological changes were studied by routine histological methods. During sexual quiescence spermatogenesis was arrested. The regressive seminiferous tubules consisted predominantly of Sertoli cells and spermatogonia. On the other hand, histological quantification suggested that season has no significant effects on the number or the nuclear dimensions of Leydig cells in this species. The capacity of the regressive testes (per unit weight) to metabolize P and DHA to testosterone (T) was somewhat greater in regressive (48.5%, 49.4%) than in active (33.2%, 41.6%) testes. The results also suggest that the greater in vitro T production encountered during reproductive quiescence is due possibly to an increase in the activity of 17 beta-hydroxysteroid dehydrogenase (per unit weight). Our data on Leydig cell numbers indicate, however, that the capacity of the individual Leydig cells to produce T is decreased during sexual regression. T. europaea appears to be quite exceptional among seasonally breeding small mammals exhibiting pronounced annual changes in spermatogenesis in that the testes retain a considerable enzymatic capacity to produce testosterone from pregnanes during sexual quiescence. The results suggest that pituitary as well as paracrine regulation of the annual testicular cycle in this species differs from that generally encountered in seasonal breeders.
Gen Comp Endocrinol 1989 Nov
PMID:The testes of moles (Talpa europaea) retain a considerable microsomal capacity for androgen synthesis during seasonal regression. 253 92

The transport systems for glucose present in Candida utilis cells, growing in batch and continuous cultures on several carbon sources, have been studied. Two different systems were found: a proton symport and a facilitated diffusion system. The high-affinity symport (Km for glucose about 15 microM) transported one proton per mole of glucose and was partially constitutive, appearing in cells grown on gluconeogenic substrates such as lactate, ethanol and glycerol. It was also induced by glucose concentrations up to 0.7 mM and repressed by higher ones. The level of repression depended on the external glucose concentration at which cells had grown in a way similar to that shown by the maltose-uptake system, so both systems seem to be under a common glucose control. Initial uptake by facilitated diffusion, the only transport system present in cells growing at glucose concentrations higher than 10 mM, showed a complex kinetic dependence on the extracellular glucose concentration. This could be explained either by the presence of at least two different systems simultaneously active, one with a Km around 2 mM and the other with a Km of about 1 M, or by the allosteric or hysteretic behaviour of a single carrier whose apparent Km would oscillate between 2 and 70 mM.
J Gen Microbiol 1989 Jan
PMID:Regulation of glucose transport in Candida utilis. 277 30

Two proteins, termed P85gag-mos and P58gag, are encoded by the temperature-sensitive transformation mutant, ts110 Moloney murine sarcoma virus (MuSV). Based on temperature-shift studies, P85gag-mos is believed to be important for the transforming potential of ts110 MuSV and has been found to be associated with a thermolabile kinase activity that phosphorylates both P85gag-mos and P58gag in immune complexes. Modifications of the original kinase assay conditions are reported here that have allowed a 30-fold increase in the specific activity of P85gag-mos phosphorylated in vitro. The in vitro P85gag-mos-phosphorylating activity was found to be unresponsive to 10 microM-cAMP or 10 microM-cGMP. Addition of 1 mM-pyrophosphate, a known phosphatase inhibitor, to the reaction mixture resulted in an increased yield of phosphorylated P85gag-mos and P58gag; the molar phosphate incorporation per mole of P85gag-mos increased from 0.032 to 0.9, whereas the specific activity of in vitro-phosphorylated P58gag increased 18-fold, from 0.013 to 0.234. pH curves of the in vitro kinase reaction further confirmed the presence of phosphatase activity; in the absence of pyrophosphate, a sharp optimum at pH 4 to 5 was observed, whereas it shifted broadly to pH 7.0 in the presence of pyrophosphate. Under the latter conditions, several experiments were performed in order to determine if the kinase was associated with either gag or mos sequences of P85gag-mos. Antisera directed against p15, p12 and p30 sequences of the gag protein region of P85gag-mos yielded immune complexes that allowed phosphorylation in vitro of P85gag-mos. No phosphorylating activity was detected in immune complexes containing MuSV-124-encoded P62gag. An anti-mos serum generated against a synthetic peptide representing the predicted v-mos amino acid residues 37 to 55 recognizes P85gag-mos and allowed phosphorylation of P85gag-mos in vitro in the absence of P58gag. Peptide mapping of both phosphorylated P85gag-mos and P58gag, by using a combination of Cleveland and Western/immunoperoxidase techniques, demonstrated that P85gag-mos became phosphorylated not only on gag sequences, but also at the N-terminal portion of v-mos. Phosphoamino acid analyses of P85gag-mos and P58gag phosphorylated in vitro under these modified conditions yielded predominantly phosphoserine and lesser amounts of phosphothreonine. Metabolically 32P-labelled P85gag-mos and P58gag were also found to contain phosphoserine and phosphothreonine. Based on these results, we conclude that a cAMP-independent, serine/threonine protein kinase activity is associated with the mos sequences of P85gag-mos.
J Gen Virol 1985 Oct
PMID:A cAMP-independent serine/threonine kinase activity is associated with the mos sequences of ts110 Moloney murine sarcoma virus-encoded P85gag-mos. 299 51

Water stress plating hypersensitivity was studied in two strains of Saccharomyces cerevisiae, one of them being a mutant incapable of accumulating trehalose to significant levels. The wild-type strain was grown in a defined medium with glucose, maltose or ethanol as carbon/energy source. In each case plating hypersensitivity was demonstrated and resistance to the stress developed in the second half of the exponential growth phase. Development of resistance was accompanied by accumulation of trehalose and was apparently unrelated to glycerol content which, under these conditions, was always low. A qualitatively similar trend was observed in the mutant grown on glucose but trehalose levels remained low and recovery of stress resistance was only slight. Dinitrophenol induced trehalose breakdown in resting yeast and simultaneously induced the onset of plating hypersensitivity. A negative correlation was demonstrated between trehalose content and 'plating discrepancy' (log colony count on 'normal' agar-log colony count on stressing agar) for both strains under all experimental conditions. The correlation held for trehalose contents up to about 50 mg (g dry yeast)-1, above which the yeasts were apparently fully resistant. Trehalose was evidently a more effective compatible solute, per mole, than glycerol.
J Gen Microbiol 1988 Jun
PMID:Water stress plating hypersensitivity of yeasts: protective role of trehalose in Saccharomyces cerevisiae. 306 53

The correlation between the melting temperature of intracellular DNA, determined by differential scanning calorimetry (DSC) of whole bacteria, and its guanine + cytosine (G + C) content, was examined for 58 species of bacteria. Samples of vegetative cells were heated in a Perkin-Elmer DSC-2C at 10 degrees C min-1 from 5 to 130 degrees C, cooled to 5 degrees C and then re-heated as before. Literature values for the mole fraction of G + C, XGC, were linearly related to the temperature, Tmax, at which the reversible peak, pr, observed on the second heating run was at a maximum, via the equation XGC = (Tmax -73.8)/41.0. This equation accounted for 91.9% of the variance in XGC with 95% confidence limits of +/- 7.3%, approximately 1.6 times the corresponding uncertainty (+/- 4.5%) quoted by De Ley (Journal of Bacteriology 101, 738-754, 1970) for estimates based on the spectroscopically determined melting temperature of purified DNA. Random errors of measurement of Tmax did not greatly limit the precision of the prediction and it was concluded that factors additional to base composition affected the temperature of DNA melting within the bacterial cell. Displacement of Tmax values from the fitted line was particularly noticeable in Campylobacter, Corynebacterium and Bacterionema species and part of the residual variation appeared to be species specific, possibly caused by differences in intracellular solute concentration.
J Gen Microbiol 1988 May
PMID:The relationship between the base composition of bacterial DNA and its intracellular melting temperature as determined by differential scanning calorimetry. 319 96

Frog photoreceptor membranes contain 54,000 g of protein per mole of visual pigment chromophore, virtually all of it insoluble membrane protein. Acrylamide gel electrophoresis indicates one major polypeptide class, most likely the visual pigment apoprotein. Suspensions of these photoreceptor membranes accumulate calcium ions when ATP is present, a characteristic that may play a part in visual excitation.
J Gen Physiol 1971 Sep
PMID:Characterization and analysis of frog photoreceptor membranes. 425 72

Toad bladders were challenged with vasopressin at one temperature, fixed on the mucosa with 1% glutaraldehyde, and then subjected to an osmotic gradient at another temperature. Thus, the temperature dependence of vasopressin action on membrane permeability was distinguished from the temperature dependence of osmotic water flux. As the temperature was raised from 20 degrees to 38 degrees C, there was a substantial increase in the velocity of vasopressin action, but osmotic flux was hardly affected. In this range of temperature the apparent energy of activation for net water movement across the bladder amounted to only 1.2 kcal/mole, a value well below the activation energy for bulk water viscosity. It is suggested that osmotic water flux takes place through narrow, nonpolar channels in the membrane. When the temperature was raised from 4 degrees to 20 degrees C, both vasopressin action as well as osmotic water flux were markedly enhanced. Activation energies for net water movement were now 8.5 kcal/mole (4 degrees -9 degrees C) and 4.1 kcal/mole (9 degrees -20 degrees C), indicating that the components of the aqueous channel undergo conformational changes as the temperature is lowered from 20 degrees C. At 43 degrees C bladder reactivity to vasopressin was lost, and irreversible changes in selective permeability were observed. The apparent energy of activation for net water movement across the denatured membrane was 6.6 kcal/mole. Approximately 1 microosmol of NaCl was exchanged for 1 microl of H(2)O across the denatured membrane.
J Gen Physiol 1972 May
PMID:Temperature dependence of vasopressin action on the toad bladder. 462 51

Partially and highly purified sheep LH-releasing factor (LRF) induced secretion of LH during incubations of anterior pituitary slices from ovariectomized ewes treated vaginally or by subcutaneous injection with fluorogestone acetate. The incubation medium contained Krebs-Ringer bicarbonate buffer with glucose, amino acids, mannose, galactose, fucose, glucosamine, galactosamine, sialic acid, calf serum, penicillin, and streptomycin. First, the optimum effect of a dose of 45 mg fluorogestone daily for 12 days before slaughter was demonstrated. These tissues yielded about 2-6 mcg LH per mg tissue in 2 hours. A dose curve of LRF showed 4.7 mcg per mg tissue was optimal, and this dose was adjusted for the purity of the LRF used in subsequent experiments. Added LH, 15.5 mcg highly purified, did not lessen LH production. LH production was fairly constant for 4-5 hours, if the medium were not changed, but increased for up to 7 hours if the medium were renewed. After incubation with labeled amino acids or proline, LH was purified 26-fold over other proteins by ammonium sulfate fractionation DEAE-cellulose chromatography, and Sephadex gel filtration. This LH was biologically active by radioimmunoassay and by the ovary ascorbic acid depletion assay, and of high specific activity, 2.2 Ci per mole LH.
Gen Comp Endocrinol 1971 Aug
PMID:[In vitro action of hypothalamic luteinizing hormone releasing factor (IRF) on lamb anterior pituitary. I. Kinetics of excretion of luteinizing hormone (LH)]. 493 8

Growth of Streptococcus faecalis in a complex medium was inhibited by xenon, nitrous oxide, argon, and nitrogen at gas pressures of 41 atm or less. The order of inhibitory potency was: xenon and nitrous oxide > argon > nitrogen. Helium appeared to be impotent. Oxygen also inhibited streptococcal growth and it acted synergistically with narcotic gases. Growth was slowed somewhat by 41 atm hydrostatic pressure in the absence of narcotic gases, but the gas effects were greater than those due to pressure. In relation to the sensitivity of this bacterium to pressure, we found that the volume of cultures increased during growth in a volumeter or dilatometer, and that this dilatation was due mainly to glycolysis. A volume increase of 20.3 +/- 3.6 ml/mole of lactic acid produced was measured, and this value was close to one of 24 ml/mole lactic acid given for muscle glycolysis, and interestingly, close to the theoretic volume increase of activation calculated from the depression of growth rate by pressure.
J Gen Physiol 1968 Nov
PMID:Growth of Streptococcus faecalis under high hydrostatic pressure and high partial pressures of inert gases. 497 26


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