共查询到20条相似文献,搜索用时 46 毫秒
1.
Andrew Ricci Karen M. Sanders Julia Portmore William G. Van der Kloot 《Life sciences》1975,16(1):177-184
1. The ionophore X-537A increases the rate of catecholamine release from the frog adrenal.2. The ratio of epinephrine/norepinephrine measured during X-537A stimulation was the same as that during spontaneous release.3. Even when Ca++ was removed from the Ringer, X-537A stimulated catecholamine release, but depolarization by elevated extra-cellular K+ was no longer effective.4. X-537A also increases the release of dopamine β-hydroxylase, suggesting that the ionophore acts, at least in part, by stimulating the exocytosis of the chrommaffin granule contents.5. Therefore, it is questionable whether the release of catecholamines by X-537A is owing to its action as a Ca++- ionophore.6. The divalent cation ionophore, A-23187 (50μM), did not affect the rate of catecholamine release. 相似文献
2.
Zoospores of the fungus , pre-labeled with 45Ca, excreted up to 30% of their total 45Ca when stimulated to encyst. Excretion was essentially completed within 90 sec of the application of the stimulus. Encystment of the population was completed within 5 min. Four different stimuli were used: pectin addition (420 μg ml?1), Sr2+ addition (5 mM), cyclic AMP addition (6.7 mM) and mechanical agitation. The kinetics and amount of Ca excretion were essentially the same in each case. The calcium ionophore A23187 increased the rate of 45Ca uptake by motile zoospores, incubated in 100 μM CaCl2, but did not induce encystment under these conditions. The ionophore did not induce 45Ca efflux from pre-labeled zoospores. Incubation in EGTA and in K+ failed to induce either encystment or 45Ca excretion. We conclude that rapid excretion of a significant proportion of the zoospore calcium is linked to the early stage of stimulus-induced encystment, and that this comes from an intracellularly located, non-cytoplasmic source, such as the peripheral vesicles, but that changes in cellular Ca2+ are not necessarily the single controlling factor in the induction of encystment. 相似文献
3.
Guanylate cyclase from crude homogenates of vegetative has been characterized. It has a pH optimum of 8.0, temperature optimum of 25°C and requires 1 mM dithiothreitol for optimal activity. It strongly prefers Mn++ to Mg++ as divalent cation, requires Mn++ in excess of GTP for detectable activity, and is inhibited by high Mn++ concentrations. It has an apparent Km for GTP of approximately 517 μM at 1 mM excess Mn++.The specific activity of guanylate cyclase in vegetative homogenates is 50–80 pmoles cGMP formed/min/mg protein. Most of the vegetative activity is found in the supernatant of a 100,000 x g spin (S100). The enzyme is relatively unstable. It loses 40% of its activity after 3 hours storage on ice. Enzyme activity was measured from cells that had been shaken in phosphate buffer for various times. It was found that the specific activity changed little for at least 8 hours. Cyclic AMP at 10?4 M did not affect the guanylate cyclase activity from crude homogenates of vegetative or 6 hour phosphate-shaken cells. 相似文献
4.
M.E. Eldefrawi N. Shaker N.A. Mansour J.E. Warnick E.X. Albuquerque 《Life sciences》1981,29(10):1033-1037
Biochemical and electrophysiological studies were conducted on the electric organ of the electric fish of the Nile, , in order to determine if transmission was chemically mediated. There was no binding of [3H] acetylcholine, [3H] quinuclidinyl benzilate or [3H]-perhydrohistrionicotoxin; but low acetylcholinesterase activity was observed, as was binding of [125I] α-bungarotoxin. The latter binding was detectable at 0.85 ± 0.07 pmol/g tissue, and was totally inhibited by 1 μM α-bungarotoxin or 100 μM d-tubocurarine. A tetrodotoxin-sensitive action potential was measured which was Na+- dependent. Depolarization (30–40 mV) was caused by carbamylcholine, and this was blocked by d-tubocurarine or α-bungarotoxin. The data suggest that this electric organ which may be a rich source for electrically excitable channels, is innervated by nicotonic cholinergic motoneurons, but the concentrations of acetylcholine receptors and acetylcholinesterase are very low. 相似文献
5.
Franco Renosto Norman D. Schmidt Irwin H. Segel 《Biochemical and biophysical research communications》1982,107(1):12-18
The steady-state kinetics of the NADPH + FAD-dependent reduction of nitrate by nitrate reductase from was studied at pH 6.18. At this sub-optimum pH, Vmax was about 83 units × mg protein?1 compared with 225 units × mg protein?1 at pH 7.20. All initial velocity reciprocal plot patterns at pH 6.18 as well as the NADP+/nitrate product inhibition pattern were intersecting. In contrast, the NADP(H)/nitrate plots at pH 7.20 were parallel (Renosto, F. J. Biol. Chem. , 8616, 1981). A major effect of lowering the assay pH was to change the Km for FAD from 0.17 μM at pH 7.20 to 4 μM at pH 6.18. The results suggest that nitrate reductase has a steady-state random kinetic mechanism in which kcat in the forward direction at pH 7.20 (ca. 375 sec?1) is greater that koff for the dissociation of one or more substrates. Several observations suggest that koff for FAD is extremely small at pH 7.20. 相似文献
6.
Daniel H. Riddick Anthony A. Luciano William F. Kusmik Ila A. Maslar 《Life sciences》1978,23(19):1913-1921
Relatively large amounts of immunoreactive prolactin were measured in homogenates of human decidual tissue obtained immediately after delivery of normal term pregnancies. In order to study the release and possible synthesis of prolactin by this tissue, explants of decidua were incubated for 24 hours at 37°C in oxygenated Gey's buffer containing 20% fetal calf serum. When cycloheximide was added to the medium in concentrations sufficient to prevent protein synthesis, 85–90% of the prolactin present in the tissue was released into the medium during the first 3 hours of incubation. No additional prolactin accumulated in either the medium or the tissue during the remainder of the incubation period. In the absence of cycloheximide, the prolactin concentration in the medium increased progressively during incubation, so that after 24 hours the total amount of hormone present in the tissue and medium was significantly greater than that in the tissue and medium prior to incubation (37.6 ± 9.6 ng/ml at 0 time vs 82.2 ± 7.7 ng/ml at 24 hours). When 3H-1-leucine (100 u Ci) was supplied during incubation, radioactive proteins were detected in the medium at 24 hr, 14–20% of which were specifically precipitated by antiserum to human pituitary prolactin. When aliquots of this medium were chromatographed on Sephadex G-100, 80–95% of the 3H-proteins precipitated by antiserum to pituitary prolactin eluted in the same position as did purified, iodinated pituitary prolactin. These data indicate that a species of prolactin which is identical to pituitary prolactin by the criteria of immunoprecipitation and gel chromatography is synthesized by human decidual tissue . 相似文献
7.
The specific synthesis of F mRNA directed by the F gene carried on the specialized transducing bacteriophage F, performed , is described with the use of an S180 extract from a strain carrying R?. Synthesis of F mRNA is biphasic at approximately 7 minutes. The regulation of F mRNA synthesis by the specific arginine holorepressor present in an S180 extract prepared from a strain carrying the R+ allele is described. 相似文献
8.
High-dose carbachol (10?3 M) has previously been shown to cause NaCl absorption in short-circuited rabbit ileum. The mechanism of this effect may be norepinephrine release induced by carbachol activation of presynaptic nicotinic receptors on adrenergic neurons. Norepinephrine then interacts with postsynaptic α-adrenergic receptors on intestinal mucosal cells to stimulate neutral NaCl absorption and inhibit electrogenic bicarbonate secretion. The present paper examines the intestinal ion transport effects of DMPP an agent which is more specific than carbachol on nicotinic cholinergic receptors. DMPP (10?5 M) caused a transient increase followed by prolonged depression of the short-circuit current, increased NaCl absorption and increased tissue conductance. This effect was antagonized by hexamethonium and phentolamine. It is concluded that nicotinic cholinergic agents stimulate norepinephrine release from adrenergic nerves and effect intestinal ion transport just as norepinephrine does. 相似文献
9.
Tetsuo Sawai Laura J. Crane J.O. Lampen 《Biochemical and biophysical research communications》1973,53(2):523-530
The plasma membrane-bound penicillinase of has been purified. Amino acid analysis showed no significant differences in composition between the enzyme and exopenicillinase. Enzyme purified from cultures containing H333PO4 or [3H]-glycerol contained 33P or [3H]-glycerol activity and treatment with 8 M urea, 0.2% sodium dodecyl sulfate at 80° C did not remove the 3H-activity from the enzyme protein. Trypsin readily cleaved the glycerol-containing moiety from the enzyme protein, forming enzyme with molecular weight and heat stability like that of the exoenzyme. Phospholipase D and C also produced enzyme resembling the exo-form. 相似文献
10.
This investigation was principally undertaken to test the ionic gradient hypothesis as applied to active uptake in the rabbit kidney cortical slice preparation. Efflux of from the slice was shown to be independent of external Na+ concentration. Transferring slices from a low sodium preincubation to a high sodium incubation medium containing increased intracellular concentrations of both Na+ and K+, and accumulation occurred. Transferring slices from a low sodium preincubation to a high sodium incubation medium containing ouabain and resulted in a net increase in intracellular Na+ concentration but no accumulation occurred. Different combinations of preincubation and incubation media gave a high to low array of intracellular Na+ concentrations and these directly reflected their respective uptake. These results suggest that the Na+-gradient hypothesis does not adequately explain the transport of organic acids in rabbit kidney. These results also suggest that Na+ possibly has an intracellular role through its stimulation of channeled to energizing the accumulative mechanism. 相似文献
11.
Colin W Taylor 《Cell calcium》1984,5(4):377-390
Transcellular calcium transport by the internally perfused midgut has been measured by simultaneously monitoring 45Ca removal from the perfusing saline (entry to the cells) and its appearance in the bathing saline (exit from the cells). Reduction of the Na+ gradient across the basolateral membranes of midgut epithelial cells by removal of bathing Na+ or by addition of monensin or ouabain inhibits calcium transport across the basolateral membranes. Calcium entry at the apical membranes is inhibited in parallel. The calmodulin inhibitors, trifluoperazine or calmidazolium, do not directly affect calcium transport nor do they dissociate the parallel changes in calcium entry and exit when calcium exit is inhibited. Experiments with A23187 are consistent with a role for intracellular calcium in regulating calcium entry at the apical membranes. It is suggested that calcium transport out of midgut epithelial cells is largely by Na+-Ca2+ countertransport, and that entry may be regulated by cytoplasmic calcium so that the calcium influx never exceeds the capacity of the transport mechanisms to pump it out of the cells. 相似文献
12.
John W. Wilks Kristi K. Forbes Jerome F. Norland 《Prostaglandins & other lipid mediators》1973,3(4):427-437
Prostaglandin F2α (PGF2α) did not alter the biosynthesis of progesterone by slices of luteinized rat ovaries when used in concentrations from 1 to 10,000 ng/ml of incubation medium; likewise, PGF2α did not affect the incorporation of acetate-1-14C into progestins. PGF1α, 15-keto PGF2α, and PGE1 did not alter the biosynthesis of progesterone by luteinized rat ovaries; PGE2 inhibited the production of progesterone when used at a concentration of 10 μg/ml, but not at lower doses. PGF2α in combination with luteinizing hormone (LH) enhanced the metabolism of progesterone to 20α-hydroxypregn-4-en-3-one in luteinized rat ovaries. Interestingly, PGF2α, at a high concentration of 10 μg/ml, did stimulate progesterone biosynthesis by slices of ovarian tissue from immature rats hormonally primed to simulate “pseudopregnancy,” suggesting a steroidogenic action of prostaglandins on the ovarian follicular or interstitial cell. PGF2α (10 μg/ml) did not stimulate the biosynthesis of progesterone or 20α-hydroxypregn-4-en-3-one by slices of rabbit corpora lutea or rabbit ovarian interstitial tissue. It is concluded that prostaglandins do not stimulate progestin biosynthesis in rat luteal tissue. 相似文献
13.
Interaction of lectins with a detergent-solubilized ATPase from eel electric organ was studied. Concanavalin A, which binds to α-mannosides, altered the rate of enzyme migration in agar and inhibited the formation of an antigen-antibody precipitate; other lectins had no such effects. Concanavalin A similar amounts partially inhibited ; this inhibition was reversible by α-methylglucoside. There was no corresponding effect of concanavalin A on the potassium . Concanavalin A also did not interfere with ouabain binding. Thus, concanavalin A binds to an antigenic region also involved in Na+ and/or ATP binding, but does not interact with a K+ site. 相似文献
14.
Naphthylmercaptobenzoquinone (NMBQ) inhibits photophosphorylation in chromatophores. The endogenous unsupplemented system is the most sensitive one being 50% inhibited by 0.5 μM NMBQ, whereas 20 μM are required for 50% inhibition of photophosphorylation in the presence of N-methylphenazonium methosulfate or diaminodurene. The inhibition is less effective under argon, especially in the presence of ascorbate, and is reversed on addition of various naphthoquinones, which can also reverse the inhibition of photophosphorylation by dibromothymoquinone (DBMIB). Another quinone analog, dodecylmercaptonaphthoquinone (DMNQ), inhibits endogenous photophosphorylation even more effectively than NMBQ, but its inhibition is not reversed by the added naphthoquinones. It is concluded that NMBQ and DBMIB, but not DMNQ, inhibit photophosphorylation in chromatophoresby acting as antagonists of ubiquinone. 相似文献
15.
Robert C. Richmond John D. Zimbrick 《Biochemical and biophysical research communications》1975,64(1):391-398
Cells of C thy?321 are examined for thymine residue release from DNA following gamma-irradiation from 5 to 15 krad. Experimental conditions are designed to inhibit enzyme activity that might promote base residue release. Enzyme action is restricted in order to assess the physicochemical action of radiation on cellular DNA, and to this end irradiation is done under O2, N2, and N2O saturating conditions. Both thymine and thymidine release from bacterial DNA are detected and quantitated, and three oxygen effects are noted in comparing yields of these products. No difference in effect is observed between N2 and N2O gassing conditions, suggesting that the hydroxyl radical has little effect on thymine or thymidine release from irradiated DNA . 相似文献
16.
Harald S. Hansen 《Prostaglandins & other lipid mediators》1974,8(2):95-105
15-Hydroxyprostaglandin dehydrogenase from bovine lung was purified 7.4 times to a specific activity of 1.4 mU/mg of protein. The isoelectric point was estimated to 5.4 and the molecular weight by gelfiltration to 40,000. Km for prostaglandin E1 and for NAD+ were found to be 3.4 μM and 1.1 × 10?4M respectively. The enzyme was inhibited by indomethacin and aspirin. The indomethacin inhibition was found to be non-competitive to prostaglandin E1 having a Ki=1.4 × 10?4M and a Ki′=1.6 × 10?5M. 相似文献
17.
James B. Johnston I.C. Gunsalus 《Biochemical and biophysical research communications》1977,75(1):13-19
Metabolic plasmids conferring on the aromatic growth phenotypes naphthalene, Nah+, salicylate, Sal+, or toluate, Tol+, have been isolated as covalently closed circular DNA in 100 μg amounts. Plasmid DNA was banded in CsCl-ethidium bromide density gradients and sedimentation rates measured in sucrose gradients and by analytical centrifuge. The plasmid sizes found, in millions, were /NAH 42, /SAL 43, /TOL 55, 42. Transformation of metabolic plasmid free with the isolated DNA confirmed the respective aromatic pathway gene contents. 相似文献
18.
S.A. Voelkel K.W. Stuckey C.R. Looney F.M. Enright P.E. Humes R.A. Godke 《Theriogenology》1983,19(3):355-366
Two experiments were conducted to test for the recovery of brucella organisms from uterine flushings and harvested embryos of sero-positive embryo donor females. In Experiment I, 16 sero-positive cows were superovulated with FSH treatments and artificially inseminated at 12, 24 and 36 hours following the onset of estrus with brucella-free semen. At 48 hours after the onset of estrus, one half the potential donor females were administered an intrauterine inoculation of 3.3 to 4.6 × 104 (strain 2308) organisms while the remainder received a control inoculation. In Experiment II, the same 16 cows were similarly administered superovulatory treatments and inseminated following estrus. The uterine inoculation was increased to 1.5 to 2.5 × 108 organisms administered 48 hours following estrus. Samples of recovered flushing medium and homogenized embryo residues were placed into a validated culture system to detect the presence of brucella bacteria. Uterine flushings and embryos recovered from 31 females exhibiting estrus following FSH treatments were free from either field strain or the inoculated (strain 2308) contamination. The flushings obtained from a single female, which did not respond with estrus following FSH treatment but was inoculated at appointment, did contain which was identified as the inoculated strain 2308 and not field strain organisms. These results indicate that brucella contamination of flushing media and harvested embryos will not likely be incurred when collecting embryos from sero-positive donor females. These findings offer further encouragement for the use of embryo transplantation as a method to produce brucella-free offspring from infected cows. 相似文献
19.
Fred Naider Shabbir A. Khan David D. Parker Jeffrey M. Becker 《Biochemical and biophysical research communications》1980,95(3):1187-1191
A soluble macromolecule-peptide conjugate, [(Met)3-OPEG] inhibited the uptake of Met-Met-[] Met into . Uptake of leucine into this strain was not affected by Met3-OPEG under identical conditions. Inhibition by the macromolecular inhibitor was competitive (KI = 5.1 × 10?5M)and followed the structural requirments of the peptide transport systems in and . These findings give the first example of inhibition of metabolite transport by a synthetic macromolecular competitor. 相似文献
20.
María M. Elías Elbio J. Comín Marta E. Grosman Susana A. Galeazzi Emilio A. Rodriguez Garay 《生物化学与生物物理学报:生物膜》1982,693(2):265-272
(1) The effects of unconjugated bilirubin on the accumulation of , kinetics of uptake, the efflux of pre-accumulated and water and electrolyte distribution were investigated in the rat kidney cortical slice. (2) The addition of unconjugated bilirubin to the incubation medium decreased the 60 min slice-to-medium concentration ratio of . (3) The decrease in accumulation by unconjugated bilirubin was found to be more pronounced by increasing the concentration of pigment in the medium. (4) The rate of uptake of as a function of concentration differed in aerobiosis and anaerobiosis, and unconjugated bilirubin decreased only the uptake of in aerobic conditions. (5) The efflux of pre-accumulated decreased when unconjugated bilirubin concentration in the medium was low (10–20 μM) but the efflux increased when the concentration of pigment was much higher (100 μM). (6) The addition of unconjugated bilirubin to the medium (40–100 μM) increased intracellular sodium and total tissue water content, and decreased intracellular potassium and oxygen consumption of tissue. However the slices incubated with low concentration of pigment (20 μM) did not exhibit significative changes in cellular functional parameters. (7) These findings suggest that unconjugated bilirubin impairs transport by a complex mechanism that might involve binding of pigment to sites necessary for anion transport, although effects related to pigment toxicity or to its oxidative decomposition are not excluded. 相似文献