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61.
Data from the North Pacific sperm whale (Physeter catodon Linnaeus, 1758) fishery were examined for a possible density dependent change in growth during 40 yr harvesting after World War II. Early in this period males from the eastern stock were 16.8 m or less in length. By the early 1970s the largest males in the catch exceeded 16.8 m in length and reached 18.9 m in the late 1970s. The proportion of males measuring over 16.8 m, among sexually mature males (≥14.0 m), increased from 0 to >20% during the 1970s. Increases in the maximum size of males were possibly preceded by a change in the frequency distribution of body lengths in the middle 1960s when only 10% of the postwar catch had been taken. Testis weights suggested an increase in body length at sexual maturity. Two of the three putative North Pacific stocks showed similar growth changes. Adult males taken in the Bering Sea did not show such changes during the exploitation which ended in 1972 because of overfishing. Females showed no detectable change in body size. It is concluded that: (1) density dependent effects on male growth are greater before sexual maturity than after it, (2) males may show density dependent changes even at a population level above 90% of the carrying capacity, (3) polygynous males acquire more mates and realize higher reproductive success because of increased body size, and (4) females appear to maximize production by maturing earlier and shortening calving intervals in response to density change. 相似文献
62.
Erkki Hltt Pirkko Pohjanpelto 《Biochimica et Biophysica Acta (BBA)/Molecular Cell Research》1982,721(4):321-327
We recently isolated a Chinese hamster ovary cell line which grows well without serum but requires the exogenous polyamines putrescine, spermidine or spermine for continuous replication. Here we show that these cells are defective in the arginase-catalyzed synthesis of ornithine, the precursor of polyamines, and that ornithine can replace polyamines in the medium for supporting growth of the cells. The activities of two other key enzymes of polyamine biosynthesis, ornithine decarboxylase and adenosylmethionine decarboxylase, are clearly detectable and show increase during polyamine starvation. In ornithine- and polyamine-free medium cellular putrescine and spermidine are rapidly depleted while the concentration of spermine decreases only moderately. We show further that the cells are able to grow in serum-containing medium without added ornithine or polyamines. This is explained by our finding that serum contains arginase which synthesizes ornithine from arginine in the medium. All the sera from different animal species tested contained arginase activity although in greatly varying amounts. Serum-free medium is therefore essential for expression of arginase deficiency in cells in tissue culture. The eventual importance of polyamines for serum-free cultures in general is discussed. 相似文献
63.
A new theory for the electron transfer by the non-adiabatic process is formulated taking into account the origin shift and the frequency change of the vibration. The resultant formulas are quite similar to those of Jortner (Jortner, J. (1976) J. Chem. Phys. 64, 4860–4867) except that the free energy gap ΔG is used instead of the energy gap ΔE. By applying this theory to the photosynthetic electron transfer, the role of the remarkable temperature dependence of the electron transfer from cytochrome to P+ in Chromatium vinosum and the experimental data were reproduced very well using a small value of the coupling strength in contrast with the previous theory. This implies that proteins play a role to exclude many of the solvent molecules from the region of the electron transfer reaction between the donor and acceptor molecules. The negative activation process in the back electron transfer from Q?A to P+, the very slow back electron transfer from I? to P+ and the solvent isotope effect on the cytochrome oxidation are also successfully explained by this new theory. It is shown that even a qualitative conclusion as to the molecular parameters obtained from the temperature dependence of the electron transfer is different between the present theory and that of Jortner. 相似文献
64.
T-cell function during acute Toxoplasma gondii infection was evaluated in murine models. Blastogenic response to the T-cell mitogen concanavalin A (Con A) was not depressed during infection with either the C37 or the C56 strain of T. gondii in either or mice that were inoculated either intravenously or intraperitoneally with varying doses of tachyzoites 7, 14, or 30 days earlier. In evaluation of lymphocytes from individual mice, utilization of a range of concentrations of Con A was found to be important for correct interpretation of results. There was variability in the magnitude of response of individual mice and in the concentration of mitogen that produced an optimal response among the inbred mice. The T-cell-dependent, primary antibody response to sheep red blood cells (SRBC) was not depressed in mice infected with the C37 strain of Toxoplasma 1 and 8 days prior to inoculation with SRBC. A lower blastogenic reponse to Con A of lymphocytes from mice compared with that of mice appeared to correlate with increased susceptibility of mice to low-challenge inocula of T. gondii. 相似文献
65.
Philip L. Smith Stephanie A. Orellana Michael Field M.D. 《The Journal of membrane biology》1981,63(3):199-206
Summary Unidirectional fluxes of35SO4 across and into rabbit ileal epithelium were measured under short-circuit conditions, mostly at a medium SO4 concentration of 2.4mm. Unidirectional mucosa (m)-to-serosa (s) ands-to-m fluxes (J
ms,J
sm) were 0.456 and 0.067 moles hr–1 cm–2, respectively.J
ms was 2.7 times higher in distal ileum than in mid-jejunum. Ouabain abolished net SO4 transport (J
net) by reducingJ
ms. Epinephrine, a stimulus of Cl absorption, had no effect on SO4 fluxes. Theophylline, a stimulus of Cl secretion, reducedJ
ms without affectingJ
sm, causing a 33% reduction inJ
net. Other secretory stimuli (8-Br-cAMP, heat-stable enterotoxin, Ca-ionophore A23187) had similar effects. Replacement of all Cl with gluconate markedly reducedJ
net through both a decrease inJ
ms and an increase inJ
sm. The anion-exchange inhibitor, 4-acetoamido-4-isothiocyano-2,2-sulfonic acid stilbene (SITS), when added to the serosal side, reducedJ
ms by 94%, nearly abolishingJ
net. SITS also decreasedJ
sm by 75%. Mucosal SITS (50 m) was ineffective. 4,4-diisothiocyano-2,2-sulfonic acid stilbene (DIDS) had effects similar to SITS but was less potent. Measurements of initial rates of epithelial uptake from the luminal side (J
me) revealed the following: (1)J
me is a saturable function of medium concentration with aV
max of 0.94 moles hr–1 cm–2 and aK
1/2 of 1.3mm; (2) replacing all Na with choline abolishedJ
me; (3) replacing all Cl with gluconate increasedJ
me by 40%; (4) serosal SITS had no effect onJ
me; and (5) stimuli of Cl secretion had no effect onJ
me or increased it slightly. Determination of cell SO4 with35SO4 indicated that, at steady-state, the average mucosal concentration is 1.1 mmoles per liter cell water, less than half the medium concentration. Cell SO4 was increased to 3.0mm by adding SITS to the serosal side. Despite net transport rates greater than 1.4 Eq hr–1 cm–2, neither addition of SO4 to the SO4-free medium nor addition of SITS to SO4-containing medium altered short-circuit current. The results suggest that (1) ileal SO4 absorption consists of Na-coupled influx (symport) across the brush border and Cl-coupled efflux (antiport) across the basolateral membrane; (2) the overall process is electrically neutral; (3) the medium-to-cell Cl concentration difference may provide part of the driving force for net SO4 absorption; and (4) since agents affecting Cl fluxes (both absorptive and secretory) have little effect on SO4 fluxes, the mechanisms for their transcellular transports are under separate regulation. 相似文献
66.
Abstract: Mouse brain slices take up hypotaurine (2-aminoethanesulphinic acid) from medium by means of two concentrative low- and high-affinity transport systems. [35 S]Hypotaurine uptake by the slices was significantly reduced in the absence of external potassium, calcium, or magnesium ions. An excess of potassium ions also inhibited hypotaurine uptake by one-half. Uptake was almost completely abolished on removal of sodium ions. The K m constants for both low- and high-affinity transport components increased in a low-sodium medium, suggesting that sodium ions are required when hypotaurine is attached to its possible carrier sites in plasma membranes. Sodium ions also mimicked allosteric effectors of hypotaurine transport, showing positive cooperativity. More than two sodium ions may be involved in the transport of one hypotaurine molecule across the cell membrane. The calculated activation energies of transport were fairly similar in normal and sodium-deficient media and thus sodium ions may not participate in the activation mechanisms of the transport. With respect to cation dependence, hypotaurine transport in brain slices exhibits features characteristic of neurotransmitter amino acids. 相似文献
67.
Arrhenius plots of the maximal velocities for the Ca2+ -and Mg2+ -dependent ATPase activities found in a plasma membrane-rich microsome fraction isolated from the roots of barley ( Hordeum vulgare L. cv. Conquest) were nonlinear. Arrhenius plot analyses using a relation which produced curvilinear Arrhenius plots accurately fit the data and allowed the calculation of the activation enthalpies and molar heat capacities of activation. The temperature dependence of the computed Km values for the Ca2+ - and Mg2+ -dependent ATPase activities was complex, with the highest enzyme-substrate affinities being obtained near the barley seedling growth temperature (16°C). Using electron paramagnetic resonance spectroscopy with amphiphilic cationic and anionic spin probes, it was possible to demonstrate that temperature changes and increasing Ca2+ concentrations could alter the mobility of the membrane lipid polar head groups. Inhibition of the ATPase activities by high levels of Ca2+ may result from a Ca2+-induced reduction in the lipid polar head group mobility. The possible role of lipid polar head group-protein interactions in the complex temperature dependence of the barley root ATPase kinetic constants is discussed. 相似文献
68.
Lennart Axelsson 《Physiologia plantarum》1981,53(2):125-130
Dark grown leaves of wheat were irradiated with red light of different intensities, at a temperature close to 0°C. The rate of photoreduction of the protochlorophyllide 650-form into chlorophyllide 684-form was measured. On continued irradiation the chlorophyllide 684-form was photodecomposed. By comparing the rates of the two processes the quantum yield for photooxidation of the chlorophyllide 684-form was calculated. The quantum yield was 2°10-5 at an intensity of 2200 W m-2 , and increased with decreasing light intensity to 3.2°10-5 at an intensity of 170 W m-2 . 相似文献
69.
Showdomycin inhibited pig brain ( with pseudo first-order kinetics. The rate of inhibition by showdomycin was examined in the presence of 16 combinations of four ligands, i.e., Na+, K+, Mg2+ and ATP, and was found to depend on the ligands added. Combinations of ligands were divided into five groups in terms of the magnitude of the rate constant; in the order of decreasing rate constants these were: (1), (2) , , and none, (3) , and , (4) and , , , and ATP. The highest rate was obtained in the presence of Na+, Mg2+ and ATP. The apparent concentrations of Na+, Mg2+ and ATP for half-maximum stimulation of inhibition () were 3 mM, 0.13 mM and 4μM, respectively. The rate was unchanged upon further increase in Na+ concentration from 140 to 1000 mM. The rates of inhibition could be explained on the basis of the enzyme forms present, including E1, E2, ES, E1-P and E2-P, i.e., E2 has higher reactivity with showdomycin than E1, while E2-P has almost the same reactivity as E1-P. We conclude that the reaction of ( proceeds via at least four kinds of enzyme form (E1, E2, E1 · nucleotide and EP), which all have different conformations. 相似文献
70.
Gerhard Toggenburger Max H?sermann Beat Mütsch Giulio Genoni Markus Kessler Fritz Weber Dietrich Hornig Brigitte ONeill Giorgio Semenza 《生物化学与生物物理学报:生物膜》1981,646(3):433-443
l-Ascorbate is taken up into brush border vesicles from kidney cortex of rat, rabbit and guinea pig by an efficient, Na+-dependent and potential-sensitive transport process. This uptake shows saturation () and is strongly stimulated by low concentrations of N3?. Erythorbate (d-isoascorbate) seems to be another, but poorer, substrate of the same transporter. 相似文献