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61.
Electromagnetic fields of very low amplitude have been reported to influence a number of cellular functions. Many of these
effects have a high degree of frequency specificity. Herein it is suggested that some of these reported results could be explained
by a fieldinduced alteration in the enzymic activity of integral membrane proteins. It is shown that such a field-induced
transition from an initial nonequilibrium steady-state to a final nonequilibrium steady-state can lead to an alteration in
the concentration profiles of those charged species in the cell's ambient electrolyte that comprise the so-called electrical
double layer. Examples of variations in the concentration profiles of those ions that react with a membrane-bound enzyme,
as well as nonreacting ionic species, are given. The modulation of such effects by systematic variations in extracellular
pH and ionic strength is discussed. 相似文献
62.
Optimum growth conditions for the fermentation of non-concentrated whey permeate by Kluyveromyces fragilis NRRL 665 have been defined. Use of 3.75 g yeast extract l?1, a growth temperature of 38°C and a pH of 4.0 allowed a maximum productivity of 5.23 g ethanol l?1 h?1 in continuous culture with a yield 91% of theoretical. Complete batch fermentation of permeate with 100 g lactose l?1 was possible with a maximum specific growth rate of 0.276 h?1 without any change in ethanol yield. Fermentation of concentrated permeate resulted, however, in a general decrease of specific substrate consumption rate, demonstrated by the inability to completely convert an initial 90 or 150 g lactose l?1 in continuous culture, even at dilution rates as low as 0.05 and 0.08 h?1, respectively. The decrease could be related to substrate inhibition, to an increase in osmotic pressure caused by lactose and salts, and to ethanol inhibition of both alcohol and biomass yield. The decrease in specific productivity could be counterbalanced by use of high cell density cultures, obtained by cell recycle of K. fragilis. Fermentation of a non-concentrated permeáte at a dilution rate of 1 h?1 resulted in a productivity of 22 g l?1 h?1 at 22 g ethanol l?1. Cell recycle using flocculating Kluyveromyces lactis NCYC 571 was also tested. With this strain a productivity of 9.3 g l?1 h?1 at 45 g product l?1 was attained at a dilution rate of 0.2 h?1, with an initial lactose concentration of 95 g l?1. 相似文献
63.
Effects of weak acids on proline accumulation in barley leaves: a comparison between abscisic acid and isobutyric acid 总被引:1,自引:1,他引:0
Abstract. When isobutyric acid (IBA) or abscisic acid (ABA) are supplied to leaf sections a similar rapid and marked decrease in the intracellular pH is observed. This acidification is accompanied by an increase in proline level which is about the same for both 3 mol m−3 IBA and 1 mol m−3 ABA treatments.
Fusicoccin (FC), known to act at the proton pump level, almost completely suppresses the ABA-induced acidification of the cell sap, whereas it only partially counteracts the acidifying effect of IBA, in particular during short periods of treatment. This effect of FC is paralleled by a similar inhibition of the induced proline accumulation: in fact, FC completely suppresses the ABA-induced increase in proline during short treatment periods, whereas it is only effective in inhibiting the IBA-induced proline accumulation after long treatment periods.
These data seem to suggest that the ABA- and IBA-induced changes in proline level might be mediated by changes in the intracellular pH. 相似文献
Fusicoccin (FC), known to act at the proton pump level, almost completely suppresses the ABA-induced acidification of the cell sap, whereas it only partially counteracts the acidifying effect of IBA, in particular during short periods of treatment. This effect of FC is paralleled by a similar inhibition of the induced proline accumulation: in fact, FC completely suppresses the ABA-induced increase in proline during short treatment periods, whereas it is only effective in inhibiting the IBA-induced proline accumulation after long treatment periods.
These data seem to suggest that the ABA- and IBA-induced changes in proline level might be mediated by changes in the intracellular pH. 相似文献
64.
J. Sianoudis A. C. Küsel T. Naujokat W. Offermann A. Mayer L. H. Grimme D. Leibfritz 《European biophysics journal : EBJ》1985,13(2):89-97
Energy metabolism during dark respiration of the green alga Chlorella fusca was investigated by 31P NMR spectroscopy. The kinetics of the transition from anaerobic to aerobic conditions (and vice versa) was followed with a temporal resolution of 16 s. This transition is accompanied by a shift of the cytoplasmic pH from 6.8 to 7.4, while the vacuolar pH remains constant. Simultaneously, an increase in the concentration of nucleoside-triphosphates and a decrease in the concentration of cytoplasmic orthophosphate take place, as well as the formation of mobile polyphosphates. The concentration of ATP and P
i reach steady-state levels within 30 s. Upon the reverse transition, from aerobic to anaerobic conditions, steady-state concentrations are obtained only after 3 min. 相似文献
65.
Dov Borovsky 《Archives of insect biochemistry and physiology》1985,2(2):145-159
Proteolytic enzymes were characterized in the midgut and the excreta of the stable fly Stomoxys calcitrans (L) with proteins, synthetic substrates, and inhibitors. Inhibition studies suggested trypsinlike activity in sugar-fed fly midguts, whereas excreta and blood-fed fly guts exhibited other proteases. Trypsinlike activity in midguts removed 20 and 30 h after a blood meal increased from 20% to 50% of the total proteolytic enzymes present. Trypsinlike activity was inhibited with human sera, trypsin-specific inhibitors, and a protein isolated from the stable fly thorax. When human albumin and globulin fractions were incubated with trypsinlike enzymes isolated from the midgut and excreta, the albumin fraction was less inhibitory than the globulin fractions and was readily hydrolyzed by the proteolytic enzymes. These results may indicate that the proteolytic enzymes produce an abortive complex with the globulin fractions of the sera. Such a complex may explain the temporary inhibition of proteolysis by the blood meal. Soybean trypsin inhibitor fed to stable flies caused 50% inhibition in proteolytic activity in the midguts of sugar-fed stable flies and 25% inhibition in the midguts of blood-fed stable flies. Complete inhibition of proteolytic enzyme activity was achieved only in vitro. pH profiles of proteolytic enzyme activity isolated from the excreta of blood-fed stable flies indicated that several proteolytic enzymes were excreted. 相似文献
66.
S R Carding S J Thorpe R Thorpe T Feizi 《Biochemical and biophysical research communications》1985,127(2):680-686
Immunofluorescence and immunoblotting experiments, using a monoclonal antibody to the 13 kDa mammalian beta-galactoside-binding lectin have shown that human lymphocytes contain nuclear and cytoplasmic proteins of apparent molecular masses of 130, 80, 65 and 13 kDa that are antigenically related to the lectin and whose levels and patterns of expression change in association with transformation, or after stimulation with mitogens. These observations, together with the finding that the myeloid cell line K562 is also rich in the 130 kDa component, whereas the mature granulocytes of normal donors and of patients with chronic myeloid leukaemia are lacking in all of the immunoreactive forms, raise the possibility that this family of lectin-related proteins may be components of growth regulatory systems that are variously elicited in the transformed and stimulated cells. 相似文献
67.
The pH gradient and the electric potential across the tonoplast in mechanically isolated beetroot vacuoles has been studied by following the uptake of [14C]methylamine and [14C]triphenyl-methylphosphoniumchloride. In response to Mg-ATP, the vacuolar interior is acidified by 0.8 units. This strong acidification is accompanied by a slight hyperpolarization of the membrane potential, which is probably caused by a proton diffusion potential. In preparations where only a small acidification (0.4 units) occurred, the membrane potential was depolarized by the addition of Mg-ATP. Different monovalent cations and anions were tested concerning their effect on the pH gradient and ATPase activity in proton-conducting tonoplasts. Chloride stimulation and NO
3
-
inhibition were clearly present. The observed decline of the pH gradient upon the addition of Na+ salts is probably caused by an Na+/H+ antiport system.Abbreviations and symbol CCCP
carbonylcyanide-m-chlorophenylhydrazone
- Mes
2(N-morpholino)ethanesulfonic acid
- TPMP+
triphenylmethylphosphoniumchloride
- Tris
2-amino-2-(hydroxymethyl)-1,3-propanediol
-
membrane potential
Dedicated to Professor A. Betz on the occasion of his 65th birthday 相似文献
68.
Magnus Appelberg 《Hydrobiologia》1985,121(1):19-25
During exposure to soft water, acidified to pH 4.0, the haemolymph concentrations of Na+, K+, and Cl– decreased whereas the Ca2+ concentration fluctuated in Astacus astacus. The haemocyte content of K+ decreased from 9% to 2% of the total haemolymph K+ content after exposure to pH 3.7 for 3 days. Within 14 days, 250 µg Al3+ l–1, as Al2(SO4)3 at pH 5.0, reduced the haemolymph Na+ content in Astacus astacus and Pacifastacus leniusculus, however, the effects were less pronounced than earlier reported for fish. Disturbed ion regulation, mainly depending on low pH, is thought to contribute to the absence of these species in acid waters. 相似文献
69.
Marshall H. Montrose Geraldine Bebernitz George A. Kimmich 《The Journal of membrane biology》1985,88(1):55-66
Summary The experiments reported here evaluate the capability of isolated intestinal epithelial cells to accomplish net H+ transport in response to imposed ion gradients. In most cases, the membrane potential was kept constant by means of a K+ plus valinomycin voltage clamp in order to prevent electrical coupling of ion fluxes. Net H+ flux across the cellular membrane was examined at pH 6.0 (the physiological lumenal pH) and at pH 7.4 using methylamine distribution or recordings of changes in media pH. Results from both techniques suggest that the cells have an Na+/H+ exchange system in the plasma membrane that is capable of rapid and sustained changes in intracellular pH in response to an imposed Na+ gradient. The kinetics of the Na+/H+ exchange reaction at pH 6.0 [K
t
for Na+=57mm,V
max=42 mmol H+/liter 3OMG (3-O-methylglucose) space/min] are dramatically different from those at pH 7.4 (K
t
for Na+=15mm,V
max=1.7 mmol H+/liter 3OMG space/min). Experiments involving imposed K+ gradients suggest that these cells have negligible K+/H+ exchange capability. They exhibit limited but measurable H+ conductance. Anion exchange for base equivalents was not detected in experiments performed in media nominally free of bicarbonate. 相似文献
70.
Göran Wingstrand 《Physiologia plantarum》1985,64(2):223-229
Membrane-bound MgATPase activity from roots of young sugar beet ( Beta vulgaris L. cv. Monohill) was investigated in a membrane fraction purified by partition in an aqueous polymer two-phase system. After two steps of "washing" with fresh bottom phase (rich in dextran), the polyethylene glycol rich top phase (U3 ) was practically free of mitochondrial membranes (cytochrome oxidase), and the remaining MgATPase activity showed high substrate specificity for ATP. An optimum for the MgATPase activity was found at pH 7. The activation by Na+ or K+ was strongest on the acid side without any observable shift in pH optimum. Oligomycin had no effect, but vanadate strongly inhibited the U3 MgATPase and the K+ activation was lost. The complex activation pattern achieved by varying the Na+ /K+ ratio at constant total concentration was interpreted as a synergistic (Na+ + K+ )-activation. The U3 fraction MgATP-ase activity showed a 4-fold increase in the presence of 0.01% Triton X-100 implying that the MgATPase activity is located in vesicles of which 75% or more are sealed with the ATP binding site on the inside. Comparison with the properties of plasma membrane. ATPases from other plants indicated that the U3 fraction MgATPase was mainly of plasma membrane origin. 相似文献