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1.
Transport of H+, K+, Na+ and Ca++ in Streptococcus 总被引:6,自引:0,他引:6
D. L. Heefner 《Molecular and cellular biochemistry》1982,44(2):81-106
Summary The streptococci differ from other bacteria in that cation translocations (with the possible exception of one of the K+ uptake systems) occur by primary transport systems, i.e., by cation pumps which use directly the free energy released during hydrolysis of chemical bonds to power transport. Transport systems in other bacteria, especially for Na+ and Ca++, are often secondary, using the free energy of another ion gradient to drive cation transport. In streptococci H+ efflux occurs via the F1F0-ATPase. This enzyme is composed of eight distinct subunits. Three of the subunits are embedded in the membrane and form a H+ channel; this is called the F0 portion of the enzyme. The other five subunits form the catalytic part of the enzyme, called F1, which faces the cytoplasm and can easily be stripped from the membrane. Physiologically, this enzyme functions as a H+-ATPase, pumping protons out of the cell to form an electrochemical proton gradient,
. The F1F0-ATPase, however, is fully reversible and if supplied with Pi, ADP and a
+ of sufficient magnitude (ca –200 mv) catalyzes the synthesis of ATP.
Streptococcus faecalis can accumulate K+ and establish a gradient of 50 000:1 (in>out) under some conditions. Uptake occurs by two transport systems. The dominant, constitutive system requires both an electrochemical proton gradient and ATP to operate. The minor, inducible K+ transport system, which has many similarities to the K+-ATPase of the Kdp transport system found in Escherichia coli, requires only ATP to power K+ uptake.Sodium extrusion occurs by a Na+/H+-ATPase. Exchange is electroneutral and there is no requirement for a
. The possibility that the Na+/H+-ATPase may consist of two parts, a catalytic subunit and a Na+/H+ antiport subunit, is suggested by the finding that damage to the Na+ transport system either through mutation or protease action leads to the appearance of
-requiring Na+/H+ antiporter activity.Ca++ like Na+ is extruded from metabolizing, intact cells. Transport requires no
but does require ATP. Reconstitution of Ca++ transport activity with accompanying Ca++-stimulated ATPase activity into proteoliposomes suggests that Ca++ is transported by a Ca++-translocating ATPase.Where respiring organelles and bacteria use secondary
transport systems the streptococci have developed cation pumps. The streptococci, which are predominantly glycolyzing bacteria, generate a
much inferior to that of respiring organisms and organelles. The cation pumps may have developed simply in response to an inadequate
.Abbreviations
electrochemical potential of protons
-
membrane potential
- pH
pH gradient
- p
proton-motive force
- DCCD
N,Na1-dicyclohexlcarbodiimide
- TCS
tetrachlorosalicylanilide
- FCCP
carbonylcyanide-p-trifluoromethylphenylhydrazone
- CCCP
carbonylcyanie-m-chlorophenylhydrazone
- TPMP+
triphenylmethyl phosphonium ion
- DDA+
dibenzyldimethylammonium ion
- Hepes
4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid
- EGTA
ethyleneglycol-bis (amino-ethyl-ether)-N,N-tetraacetic acid 相似文献
2.
Thermoregulation,gas exchange,and ventilation in Adelie penguins (Pygoscelis adeliae) 总被引:1,自引:0,他引:1
Mark A. Chappell Sherrie L. Souza 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1988,157(6):783-790
Summary Adelie penguins (Pygoscelis adeliae) experience a wide range of ambient temperatures (T
a) in their natural habitat. We examined body temperature (T
b), oxygen consumption (
), carbon dioxide production (
), evaporative water loss (
), and ventilation atT
a from –20 to 30 °C. Body temperature did not change significantly between –20 and 20°C (meanT
b=39.3°C).T
b increased slightly to 40.1 °C atT
a=30°C. Both
and
were constant and minimal atT
a between –10 and 20°C, with only minor increases at –20 and 30°C. The minimal
of adult penguins (mean mass 4.007 kg) was 0.0112 ml/[g·min], equivalent to a metabolic heat production (MHP) of 14.9 Watt. The respiratory exchange ratio was approximately 0.7 at allT
a. Values of
were low at lowT
a, but increased to 0.21 g/min at 30°C, equivalent to 0.3% of body mass/h. Dry conductance increased 3.5-fold between –20 and 30°C. Evaporative heat loss (EHL) comprised about 5% of MHP at lowT
a, rising to 47% of MHP atT
a=30°C. The means of ventilation parameters (tidal volume [VT], respiration frequency [f], minute volume [I], and oxygen extraction [
]) were fairly stable between –20 and 10°C (VT did not change significantly over the entireT
a range). However, there was considerable inter- and intra-individual variation in ventilation patterns. AtT
a=20–30°C,f increased 7-fold over the minimal value of 7.6 breaths/min, and I showed a similar change.
fell from 28–35% at lowT
a to 6% atT
a=30°C.Abbreviations
C
thermal conductance
-
EHL
evaporative heat loss
-
oxygen extraction
-
f
respiratory frequency
-
MHP
metabolic heat production
-
evaporative water loss
-
LCT
lower critical temperature
-
RE
respiratory exchange ratio
-
T
a
ambient temperature
-
T
b
body temperature
-
rate of oxygen consumption
-
rate of carbon dioxide production
- I
inspiratory minute volume
-
VT
tidal volume 相似文献
3.
Summary The rate of inorganic carbon uptake and its steadystate accumulation ratio (intracellular/extracellular concentration) was determined in the cyanobacteriumAnabaena variabilis as a function of extracellular pH. The free energy of protons (
) across the plasmalemma was calculated from determinations of membrane potential, and intracellular pH, as a function of the extracellular pH. While inward proton motive force decreased with increasing extracellular pH from 6.5 to 9.5, rate of HCO
3
–
influx and its accumulation ration increased. The latter is several times larger than would be expected should HCO
3
–
influx be driven by
. It is concluded that HCO
3
–
transport in cyanobacteria is not driven by the proton motive force. 相似文献
4.
Bioenergetics: the evolution of molecular mechanisms and the development of bioenergetic concepts 总被引:1,自引:0,他引:1
Vladimir P. Skulachev 《Antonie van Leeuwenhoek》1994,65(4):271-284
Possible routes for the evolution of cell energetics are considered. It is assumed that u.v. light was the primary energy source for the precursors of the primordial living cell and that primitive energetics might have been based on the use of the adenine moiety of ADP as the u.v. chromophore. It is proposed that the excitation of the adenine residue facilitated phosphorylation of its amino group with subsequent transfer of a phosphoryl group to the terminal phosphate of ADP to form ATP. ATP-driven carbohydrate synthesis is considered as a mechanism for storing u.v.-derived energy, which was then used in the dark. Glycolysis presumably produced compounds like ethanol and CO2 which easily penetrate the membrane and therefore were lost by the cell. Later lactate-producing glycolysis appeared, the end product being non-penetrant and, hence, retained inside the cell to be utilized to regenerate carboxydrates when light energy became available. Production of lactate was accompanied by accumulation of equimolar H+. To avoid acidification of the cell interior, an F0-type H+ channel was employed. Later it was supplemented with F1. This allowed the ATP energy to be used for uphill H+ pumping to the medium, which was acidified due to glycolytic activity of the cells.In the subsequent course of evolution, u.v. light was replaced by visible light, which has lower energy but is less dangerous for the cell. It is assumed that bacteriorhodopsin, a simple and very stable light-driven H+ pump which still exists in halophilic and thermophilic Archaea, was the primary system utilizing visible light. The
formed was used to reverse the H+-ATPase, which began to function as H+-ATP-synthase. Later, bacteriorhodopsin photosynthesis was substituted by a more efficient chlorophyll photosynthesis, producing not only ATP, but also carbohydrates. O2, a side product of this process, was consumed by the H+-motive respiratory chain to form
in the dark. At the next stage of evolution, a parallel energy-transducing mechanism appeared which employed Na+ instead of H+ as the coupling ion (the Na+ cycle). As a result, the bioenergetic system became more stable under unfavorable conditions. Apparently, the latest inventions of evolution of biological energy transducers are those which can utilize
and
outside the coupling membrane, like the bacterial flagellar motor and the TonB-mediated uphill transport of solutes across the outer membrane of bacteria. 相似文献
5.
Julian I. Schroeder 《The Journal of membrane biology》1989,107(3):229-235
Summary A quantitative analysis of the time and voltage dependence of outward-rectifying K+ currents (
) in guard cells fromVicia faba is described using the whole-cell patch-clamp technique. After step depolarizations from –75 mV to potentials positive to –40 mV, time-dependent outward currents were produced, which have recently been identified as K+ channel currents. This K+ current was characterized according to its time dependence and its steady-state activation.
could be described in terms of a Hodgkin-Huxley type conductance. Activation of the current in time was sigmoid and was well fitted by raising the activation variable to the second power. Deactivating tail currents were single exponentials, which suggests that only one conductance underlies this slow outward K+ current. Rates of channel closing were strongly dependent on the membrane potential, while rates of channel opening showed only limited voltage dependence leading to a highly asymmetric voltage dependence for channel closing and opening. The presented analysis provides a quantitative basis for the understanding of
channel gating and
channel functions in plant cells. 相似文献
6.
Summary The requirement for Na+ and Cl– in the bathing media to obtain a maximal HCO
3
–
secretory flux (
) across isolated short-circuitedAmphiuma duodenum was investigated using titration techniques and ion substitution. Upon substitution of media Na+ with choline, HCO
3
–
secretion was markedly reduced. Replacement of media Cl– produced a smaller reduction of
. The presence of Cl– enhanced HCO
3
–
secretion only if Na+ was also in the media. Elevation of media Na+ or Cl– in the presence of the other ion produced a saturable increase of
. In the presence of Na+, Cl– stimulated
when added to the mucosal but not the serosal medium. In the presence of Cl–, Na+ elevated
when added to the serosal but not the mucosal medium. The ability of mucosal Cl– to stimulate
was not apparently dependent on mucosal Na+. Simultaneous addition of 10mm Cl– to the Na+-free mucosal medium and 10mm Na+ to the Cl–-free serosal medium stimulated
above levels produced by serosal Na+ alone. In conclusion, intestinal HCO
3
–
secretion required mucosal Cl– and serosal Na+ and did not involve mucosal NaCl cotransport. The results are consistent with a mucosal Cl– absorptive mechanism in series with parallel basolateral Na+–H+ and Cl––HCO
3
–
exchange mechanisms. 相似文献
7.
A small catchment on the Swedish West Coast has been studied over four years to determine S dynamics by using S isotope ratios. A Norway spruce dominated forest covers the catchment, and small peat areas occur in the lower parts of the catchment. The runoff
values varied both during the year, and from year to year. Over the period from February 1990 to December 1993, the
values ranged from — 1%. to +11%. Over the same period, the throughfall
values ranged from +1%. to +15%. There was no correlation (r
2= 0.01; Pr(F)=0.57) between
values in throughfall and runoff. Since the only input of S to the catchment is atmospheric deposition, the long-term runoff S mass flux is controlled by the deposition. Therefore, processes in the catchment are responsible for the variation in the runoff
values. During periods with
enriched runoff, bacterial dissimilatory SO
4
2–
reduction occurs in the catchment. After very dry periods, oxidation of this reduced S, which is32S-enriched, can be traced in runoff. Previous studies of the catchment have not been able to distinguish between: 1) oxidation of reduced S and dry deposition, and 2) reduction and adsorption. From the current study, it can be concluded that adsorption and dry deposition cannot cause the observed variation in runoff
. 相似文献
8.
Methanobacterium thermoautotrophicum was grown in continuous culture in a fermenter gassed with H2 and CO2 as sole carbon and energy sources, and in a medium which contained either NH4Cl or gaseous N2 as nitrogen source. Growth was possible with N2. Steady states were obtained at various gas flow rates with NH4Cl and with
and the maintenance coefficient varied with the gas input and with the nitrogen source. Growth of Methanococcus thermolithotrophicus in continuous culture in a fermenter gassed with H2, CO2 as nitrogen, carbon and energy sources was also examined.Abbreviations
molecular growth yield (g dry weight of cells per mol of CH4 evolved)
-
growth rate (h-1)
-
D
dilution rate (h-1)
- rate (h-1);
relation of Neijssel and Tempest and of Stouthamer and Bettenhaussen
-
energy 相似文献
9.
Henrik Laasch 《Planta》1989,178(4):553-560
A series of tertiary amines was investigated for effects on the transmembrane proton potential difference (
H), on photophosphorylation and on electron-flux control related to the intrathylakoid proton potential (
HI), using isolated chloroplasts ofSpinacia oleracea L. As indicated by 9-aminoacridine fluorescence and [14C]methylamine uptake, all amines studied inhibited a build-up of
H and, in parallel, ATP synthesis. Even when
H was low, strong
H1-dependent electron-flux control was observed under the influence of tertiary amines. The strength of flux control in the presence of low
H and the effectiveness of inhibition of ATP synthesis linearly increased with the lipophilicity of the amines. The most effective of the amines tested caused 50% inhibition of ATP synthesis at a concentration of 6 M, which is about 1000-fold lower than the concentration required for inhibition by methylamine. The data presented indicate the existence of two proton domains in the thylakoid vesicles, one of them feeding the ATP-synthase, the other the sites of pH-dependent electron-flux control. It is concluded that tertiary amines develop their action in a lipophilic domain of the thylakoid membrane, in the vicinity of the ATP-synthase complex. A mechanism for selective uncoupling and for the maintenance of
HI-dependent electron flux control in the presence of low
H is discussed.Abbreviations and symbols
coefficient for pH-dependent electron flux control
- 9-AA
9-aminoacridine
- Chl
chlorophyll
- I50
amine concentration producing 50% inhibition of ATP-synthesis
- Je
flux of photosynthetic electron transport
-
k
H
apparent rate constant for proton efflux
-
H1
proton potential in the thylakoid lumen
-
H1
transthylakoid proton potential difference
-
p
partition coefficient
-
q
AA
coefficient for 9-aminoacridine fluorescence quenching
- PS
photosystem
- Q
quantum flux of photosynthetically active light
Dedicated to Professor Wilhelm Simonis, on the occasion of his 80th birthday 相似文献
10.
The growth yield of Chlorella vulgaris, Y
kJ defined as g cells harvested per kJ of light energy absorbed by the cells, was assessed in a turbidostat culture by varying CO2 and O2 partial pressures (
and
). The value of Y
kJ ranged from 3.1×10-3 to 5.0×10-3 g cells/kJ under light-limited conditions [
= 1.02.4%,
= 065%; total pressure of gas (composed of CO2, O2 and N2)=1 atm]. In the light-limited environment, the algal specific growth rate deteriorated appreciably with the increase of
. The deterioration accounts for the above range of Y
kJ observed. The growth inhibition due to oxygen that was defined by subtracting from 1.0 the ratio of at given values of
to that at
= 0% extended from 0.07–0.30 (7–30%). However, glycolate could not be detected in the turbidostat culture. Isotopic experiments on the specific rate of 14CO2 uptake also revealed that the inhibition due to oxygen was from 22–38% when
was varied from 0 to nearly 100%. These effects of oxygen were discussed, referring to the activity of ribulose-1,5-bisphosphate carboxylase that is inhibited competitively by oxygen.Non-Standard Abbreviations INH
isonicotinic acid hydrazide
- PPO
2,5-diphenyloxazole
- DCMU
3-(-3,4-dichlorophenyl)-1,1-dimetylurea
- CA
carbonic anhydrase
- RuP2
ribulose-1,5-bisphosphate 相似文献
11.
Summary
D. melanogaster males of
bb/O genetic constitution undergoing rDNA magnification were mated singly to XXbb
+/O females, yielding
bb/O male progeny, and to XNO-w sn bb
+ fameles, yielding
bb/XNO- females. The male and female offspring were scored for the bb
+ phenotype.Results show that there is a higher percentage of bb
+ flies in the
bb/O male progeny than in
bb/XNO- females progeny, in single crosses as well as in the combined data. rRNA/DNA hybridization experiments agree with this observation, by showing that the rDNA content in the progeny of premagnified flies was higher in the sons than in the daughters.These data indicate that the increase of ribosomal RNA genes is not due to a stable event such as an unequal mitotic sister exchange, whereas they do not contrast with the extracopy model. 相似文献
12.
During peak thermogenesis of anthesis, high rates of respiration by the sterile male florets on the spadix ofPhilodendron selloum significantly reduce the oxygen tension (PO
2) and raise CO2 tension between the florets. Nevertheless, respiration is not limited by the availability of O2 under natural conditions. At experimental PO
2 below about 17 kPa, however, florets begin to show decreased O2 consumption. A respiratory exchange ratio of 0.83 indicates that the major energy source is not starch, but is probably lipid.Abbreviations and symbols
capacitance of the gas phase for O2 (ml O2 cm-3 kPa-1)
- DO
2
binary diffusion coefficient of O2 in air (cm2 min-1)
- KO
2
Krogh's diffusion coefficient (ml O2 cm-2 min-1 kPa-1 cm)
- PO
2 PCO
2
partial pressures of O2 and CO2 (kPa)
-
rate of O2 consumption (ml O2 g-1 h-1)
- Fgas
fractional gas volume
- P80
O2 partial pressure at which
falls below 80% of maximum
- RE
respiratory exchange ratio
相似文献
13.
P. Pic 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1978,123(2):155-162
Summary In seawater (SW)-adaptedMugil andFundulus, gill effluxes of Na+
and of Cl–
and the simultaneously recorded transgill potential (P.D.) differ according to whether they are measured in stressed or rested animals.In rested animals of the two species, transfer to Ringer's solution considerably reduces the P.D. but not
. InFundulus,
is also decreased. Transfer of the two species from SW to fresh water (FW) reduces
and
by 75 to 85% and leads to a large inversion of P.D. When K+ is added to FW, a gill depolarization occurs, as well as a large increase of
and
.These results suggest that: 1) the P.D. originates primarily from the diffusion of cations, the gill permeability to Na+ (
) being greater than that to Cl– (
), 2) a Cl–/Cl– exchange independent of P.D. is associated with the Cl– pump; 3) Cl– pump activity is linked to Na+/K+ exchange which in turn is associated to a Na+/Na+ exchange diffusion mechanism.In stressed individuals of the two species, the P.D. in SW, as well as the P.D. changes observed during transfer experiments, are considerably reduced. The decrease of
and
observed after transfer from SW to FW are also minimised. Changes are smaller inFundulus. The decrease of P.D. characterizing stressed animals may be at least in part due to a 3 to 4 fold increase of
which becomes equal to
in both species.As a result of stress, the K+-activated Na+ and Cl– excretion mechanisms are totally inhibited inFundulus and partially so inMugil.Stress response seems more intense inFundulus and recovery from stress faster inMugil. 相似文献
14.
B. Culik A. J. Woakes D. Adelung R. P. Wilson N. R. Coria H. J. Spairani 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1990,160(1):61-70
Summary The energy requirements of Adélie penguin (Pygoscelis adeliae) chicks were analysed with respect to body mass (W, 0.145–3.35 kg, n=36) and various forms of activity (lying, standing, minor activity, locomotion, walking on a treadmill). Direct respirometry was used to measure O2 consumption (
) and CO2 production. Heart rate (HR, bpm) was recorded from the ECG obtained by both externally attached electrodes and implantable HR-transmitters. The parameters measured were not affected by hand-rearing of the chicks or by implanting transmitters. HR measured in the laboratory and in the field were comparable. Oxygen uptake ranged from
in lying chicks to
at maximal activity, RQ=0.76. Metabolic rate in small wild chicks (0.14–0.38 kg) was not affected by time of day, nor was their feeding frequency in the colony (Dec 20–21). Regressions of HR on
were highly significant (p< 0.0001) in transmitter implanted chicks (n=4), and two relationships are proposed for the pooled data, one for minor activities (
), and one for walking (
). Oxygen consumption, mass of the chick (2–3 kg), and duration of walking (T, s) were related as
, whereas mass-specific O2 consumption was related to walking speed (S, m·s-1) as
.Abbreviations
bpm
beats per minute
-
D
distance walked (m)
-
ECG
electrocardiogram
-
HR
heart rate (bpm)
-
ns
number of steps
-
RQ
respiratory quotient
-
S
walking speed (m·s-1)
-
T
time walked (s)
-
W
body mass (kg) 相似文献
15.
Beta-adrenergic control of blood oxygen affinity in acutely hypoxia exposed rainbow trout 总被引:1,自引:1,他引:0
Tetens Vilhelm Christensen Niels Juel 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1987,157(5):667-675
Summary Acute exposure of rainbow trout to hypoxic water (
=40 mmHg, 15 °C) caused a significant (P<0.01) increase in blood O2 affinity, from the normoxicP
50 value (at pHe 7.93) of 23.2±1.1 mmHg to about 19 mmHg, within 5 min. Specimens injected with the -antagonist propranolol showed no change in bloodP
50, despite a more pronounced reduction of arterial
during the hypoxic exposure.The change in bloodP
50 coincided with an increase in plasma catecholamines, notably noradrenaline. There was no change in the molar ratios of ATPHb4 and GTPHb4. The altered bloodP
50, however, correlated with an alkalinization and an increased sodium concentration of the red cells. This red cell alkalinization can be explained by -adrenergic stimulation of a membrane bound Na+/H+ antiporter.Propranolol injection into normoxic resting trout caused a significant decrease in
and increase in
indicating -adrenergic control of gas exchange in the gills. 相似文献
16.
Respiratory evaporation in panting fowl: Partition between the respiratory and buccopharyngeal pumps
John Brackenbury Peter Avery Michael Gleeson 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1981,145(1):63-66
Summary Ventilation (V) and respiratory water loss
were measured in domestic fowlGallus gallus subjected to raised environmental temperatures (33±2°C) and breathing air, 8% O2 in N2, 3% CO2 in air or 5% CO2 in air. Birds breathing air underwent an 18.6-fold increase in respiratory frequency and a 5-fold reduction in tidal volume and panting was accompanied by vigorous gular flutter. Hypoxic and hypercapnic birds breathed more slowly and deeply and gular flutter was strongly inhibited. The
ratio was similar to that predicted on the basis of the measured ventilation assuming saturation of expired gas at measured gular mucosal temperature in hypoxic and hypercapnic birds but 54% greater than the predicted value in birds panting in air. It is concluded that the excess water loss during normal panting results from tidal airflow generated independently by the buccopharyngeal pump and that buccopharyngeal ventilation is equivalent to 54% of the respiratory ventilation. 相似文献
17.
Stephen C. Wood Kjell Johansen Mogens L. Glass G. M. O. Maloiy 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1978,127(4):331-336
Summary Oxygen consumption
was measured at rest and during spontaneous activity at body temperatures of 25 and 35°C in 14 fasting Savanna monitor lizards,Varanus exanthematicus ranging in weight from 172 to 7500 g. The allometric relationship between metabolic rate at 25°C and body weight (W) is given by:
(ml O2 STPD·g–1·hr–1)=0.88W
–0.43 (Fig. 2). Although statistical comparisons are equivocal, this intraspecific size dependence exceeds that reported for interspecific comparisons among reptiles and other vertebrate groups (Fig 3). A reproducible diurnal pattern of activity was observed in undisturbed animals with minimum values of
between 2400 and 0800 h (Fig. 1). Spontaneous activity and
generally reached peak values between 1200 and 2000 hrs. The average ratio of active aerobic metabolic rate (AMR) to minimum (standard) aerobic metabolic rate (SMR) was 8.2. This voluntary AMR/SMR inVaranus exceeds the AMR/SMR for most reptiles stimulated to exhaustion. The high aerobic capacity is consistent with other evidence for efficient exchange and transport of respiratory gases inV. exanthematicus; e.g., low or absent intracardiac shunt flow resulting in high arterial saturation and low ventilation
and perfusion
requirements. 相似文献
18.
Jürgen M. Schmidt Richard R. Ernst Saburo Aimoto Masatsune Kainosho 《Journal of biomolecular NMR》1995,6(1):95-105
Summary A simple heteronuclear relayed E.COSY pulse sequence with a minimum number of pulses is proposed for the quantitative determination of heteronuclear three-bond J-coupling constants in uniformly 13C-enriched polypeptide samples. Numerous heteronuclear three-bond coupling constants, including
,
,
, and
, can be determined for each residue from a single heteronuclear relayed E.COSY spectrum. Couplings relevant for stereospecific assignments as well as for the determination of dihedral angles in the amino acid backbone and in side chains are obtained. The method is demonstrated on the uniformly 13C-enriched decapeptide antamanide (-Val1-Pro2-Pro3-Ala4-Phe5-Phe6-Pro7-Pro8-Phe9-Phe10-). 相似文献
19.
M. J. Beilby 《The Journal of membrane biology》1981,62(3):207-218
Summary The changes in the cytoplasmic Cl– concentration, [Cl–]
c
, are monitored at the time of withdrawal (starvation) and subsequent replacement of Cl– in the outside medium. The measurement technique exploits the involvement of Cl– inChara excitation. The transient clamp current due to Cl–,I
Cl, is separated from other excitation transients through Hodgkin-Huxley (HH) equations, which have been adjusted toChara. TheI
Cl amplitude depends on HH parameters, [Cl–]
c
and the maximum membrane conductance to Cl–,
. The results are discussed in terms of these quantities.I
Cl and
were found to fall after 6–10 hr of Cl– starvation, thus supporting the hypothesis that [Cl–
c
decreases in Cl–-free medium. The best HH fit to starved data was obtained with [Cl–
c
=3.5mm. The time-course forI
Cl decline is considerably slower than the time-course of the rise of the starvation-stimulated influx. As cells starved for periods longer than 24 hr are re-exposed to Cl–, it is revealed that while [Cl–]
c
remains low during long starvation,
increases to values greater than those of the normal cells. Such differences among cells starved for various lengths of time have not been detected previously. 相似文献
20.
Gill function in an elasmobranch 总被引:1,自引:0,他引:1
Gordon C. Grigg John Read 《Journal of comparative physiology. A, Neuroethology, sensory, neural, and behavioral physiology》1971,73(4):439-451
Summary Highly efficient oxygen uptake in elasmobranchs, as indicated by frequent excess of
over
has previously been ascribed to the operation of multicapillary rather than counter-current gas exchange by the gills. Analysis of models shows that, at maximum efficiency, a multicapillary system cannot account for values of
greater than
. In Port Jackson sharks Heterodontus portusjacksoni)
commonly exceeds
, which indicates the operation of a functional counter-current at the respiratory surface. The anatomical basis of this counter-current is provided by the demonstration that a continuous flow of water passes between the secondary lamellae into septal canals and thence via the parabranchial cavities to the exterior.Queen Elizabeth II Fellow. 相似文献