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Query: UMLS:C0009443 (cold)
 92,137 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The adenosinetriphosphatase (ATPase) (EC 3.6.1.3) activity in Azotobacter vinelandii concentrates in the membranous R3 fraction that is directly associated with Azotobacter electron transport function. Sonically disrupted Azotobacter cells were examined for distribution of ATPase activity and the highest specific activity (and activity units) was consistently found in the particulate R3 membranous fraction which sediments on ultracentrifugation at 144 000 X g for 2 h. When the sonication time interval was increased, the membrane-bound ATPase activity could neither be solubilized nor released into the supernatant fraction. Optimal ATPase activty occurred at pH 8.0; Mg2+ ion when added to the assay was stimulatory. Maximal activity always occurred when the Mg2+:ATP stoichiometry was 1:1 on a molar ratio at the 5 mM concentration level. Sodium and potassium ions had no stimulatory effect. The reaction kinetics were linear for the time intervals studied (0-60 min). The membrane-bound ATPase in the R3 fraction was stimulated 12-fold by treatment wiTH TRypsin, and fractionation studies showed that trypsin treatment did not solubilize ATPase activity off the membranous R3 electron transport fraction. The ATPase was not cold labile and the temperature during the preparation of the R3 fraction had no effect on activity; overnight refrigeration at 4 degrees C, however, resulted in a 25% loss of activity as compared with a 14% loss when the R3 fraction was stored overnight at 25 degrees C. A marked inactivation (although variable, usually about 60%) did occur by overnight freezing (-20 degrees C), and subsequent sonication failed to restore ATPase activity. This indicates that membrane reaggregation (by freezing) was not responsible for ATPase inactivation. The addition of azide, ouabain, 2,4-dinitrophenol, or oligomycin to the assay system resulted in neither inhibition nor stimulation of the ATPase activity. The property of trypsin activation and that ATPase activity is highest in the R3 electron transport fraction suggests that its probable functional role is in coupling of electron transport to oxidative phosphorylation.
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PMID:Characterization studies on the membrane-bound adenosine triphosphatase (ATPase) of Azotobacter vinelandii. 0 Jan 41

The high membrane potential of Acetabularia (Em=-170mV) is due to an electrogenic pump in parallel with the passive diffusion system (Ed=-80mV) which could be studied separately in the cold, when the pump is blocked. Electrical measurements under normal conditions show that the pump pathway consists of its electromotive force Ep with two elements P1 and P2 in series; P2 is shunted by a large capacitance (Cp=3mF cm-2). The nonlinear current-voltage relationship of P1 (light- and temperature-sensitive) could be determined separately; it reflects the properties of a carrier-mediated electrogenic pump. The value of Ep(-190 mV) indicates a stoichiometry of 2:1 between electrogenically transported charges and ATP. The electrical energy normally stored in Cp, compares well with the metabolic energy, stored in the ATP pool. The nonlinear current-voltage relationship of P2 (attributed to phosphorylating reactions) is also sensitive to light and temperature and is responsible for the region of negative conductance of the overall current-voltage relationship. The power of the pump (1 muW cm-2) amounts to some percent of the total energy turnover. The high Cl- fluxes (1 nmol cm-2 sec-1) and the electrical properties of the plasmalemma are not as closely related as assumed previously. For kinetic reasons, a direct and specific Cl- pathway between the vacuole and outside is postulated to exist.
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PMID:Analog circuit of the Acetabularia membrane. 0 82

Rat lens phosphofructokinase (PFK) has been found to be cold-labile at acidic pH, even in the presence of sulfate and inorganic phosphate, two known positive effectors. The inactivation appears to be an irreversible process, but can be prevented by including ATP in the incubating media. The enzyme is relatively stable at pH 8.2 incubated at 0 to 4 degrees, 25 degrees, or 37 degrees C. in the absence of the effectors, but is extremely thermolabile if the pH is lowered to 7.30 or lower. The thermolability is counteracted by many effectors, among them sulfate and ATP are the most effective. The physiologic significance of PFK instability and effector protection in the lens are discussed.
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PMID:pH-dependent temperature sensitivity of rat lens phosphofructokinase. 0 4

Blood pH in the antarctic cod (Dissostichus mawsoni) and in two Trematomus species, occlrring at --1-9 degrees C, is extremely high (approximately 8-2 to 8-3). This supports and extends Rahn's (1966) model for the temperature-pH relationship in cold-blooded vertebrates. The blood of D. mawsoni shows a low oxygen affinity (P50 approximately equal to 14-5 mmHg at pH 8-16 and -1-9 degrees C). Despite normal in vitro temperature and pH sensitivities, blood P50 increases only slightly when live fish are temperature-stressed (+ 4-0 degrees C), or become acidotic as a result of agitational stress (blood pH 7-71), primarily as a result of compensatory decreases in blood ATP levels. Oxygen-binding properties of 'stripped' (cofactor-free) solutions of D. mawsoni haemoglobin were measured in attempts to elucidate the molecular mechanisms involved in the function of the pigment.
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PMID:pH and haemoglobin oxygen affinity in blood from the Antarctic cod Dissostichus mawsoni. 1 49

Motile extracts have been prepared from Dictyostelium discoideum by homogenization and differential centrifugation at 4 degrees C in a stabilization solution (60). These extracts gelled on warming to 25 degrees Celsius and contracted in response to micromolar Ca++ or a pH in excess of 7.0. Optimal gelation occurred in a solution containing 2.5 mM ethylene glycol-bis (beta-aminoethyl ether)N,N,N',N'-tetraacetate (EGTA), 2.5 mM piperazine-N-N'-bis [2-ethane sulfonic acid] (PIPES), 1 mM MgC1(2), 1 mM ATP, and 20 mM KCI at ph 7.0 (relaxation solution), while micromolar levels of Ca++ inhibited gelation. Conditions that solated the gel elicited contraction of extracts containing myosin. This was true regardless of whether chemical (micromolar Ca++, pH >7.0, cytochalasin B, elevated concentrations of KCI, MgC1(2), and sucrose) or physical (pressure, mechanical stress, and cold) means were used to induce solation. Myosin was definitely required for contraction. During Ca++-or pH-elicited contraction: (a) actin, myosin, and a 95,000-dalton polypeptide were concentrated in the contracted extract; (b) the gelation activity was recovered in the material sqeezed out the contracting extract;(c) electron microscopy demonstrated that the number of free, recognizable F-actin filaments increased; (d) the actomyosin MgATPase activity was stimulated by 4- to 10-fold. In the absense of myosin the Dictyostelium extract did not contract, while gelation proceeded normally. During solation of the gel in the absense of myosin: (a) electron microscopy demonstrated that the number of free, recognizable F- actin filaments increased; (b) solation-dependent contraction of the extract and the Ca++-stimulated MgATPase activity were reconstituted by adding puried Dictyostelium myosin. Actin purified from the Dictyostelium extract did not gel (at 2 mg/ml), while low concentrations of actin (0.7-2 mg/ml) that contained several contaminating components underwent rapid Ca++ regulated gelation. These results indicated : (a) gelation in Dictyostelium extracts involves a specific Ca++-sensitive interaction between actin and several other components; (b) myosin is an absolute requirement for contraction of the extract; (c) actin-myosin interactions capable of producing force for movement are prevented in the gel, while solation of the gel by either physical or chemical means results in the release of F-actin capable of interaction with myosin and subsequent contraction. The effectiveness of physical agents in producting contraction suggests that the regulation of contraction by the gel is structural in nature.
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PMID:The contractile basis of amoeboid movement. V. The control of gelation, solation, and contraction in extracts from Dictyostelium discoideum. 2 Apr 47

Isolated chromaffin granules release their contents when exposed to calcium, magnesium, ATP, and high levels of chloride ions. The mechanism of release is not well-understood, but changes in anion permeability may be involved. We found that another anion, thiocyanate (SCN-), also activated release in a fashion similar to chloride, while isethionate (HO-CH2-CH2SO3-) an impermeant anion, was inactive. Mg++-ATP was found to activate the uptake of 36Cl and 14C-SCN, leading us to conclude that activation of anion uptake might be involved in the release process. The 36Cl and the 14C-SCN compartments were then compared by studying displacement of the trace anions by excess cold mass. Chloride and SCN displaced large amounts of both 36Cl and 14C-SCN, while isethionate displaced little of either tracer anion. We suggest, on the basis of these data, that ATP-mediated anion uptake may be the basis for the release mechanism. Release may occur as a consequence of anion and subsequent water uptake into granules, resulting in osmotic imbalance and osmotic shock. This may also be of physiologic importance, and we propose a cellular model for secretion based on the biochemical properties of the isolated chromaffin granule.
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PMID:Regulation of release from isolated adrenergic secretory vesicles by ATP-mediated changes in transmembrane potential and anion permeability. 2 84

We have compared the adenosine triphosphatase (ATPase) activity of mitochondria prepared from wild-type Neurospora crassa and from poky, a maternally inherited mutant known to possess defective mitochondrial ribosomes and reduced amounts of cytochromes aa3 and b. poky contains two distinct forms of mitochondrial ATPase. The first is normal in its Km for ATP, specificity for nucleotides and divalent cations, pH optimum, cold stability, and sensitivity to inhibitors (oligomycin, N,N-dicyclohexyl carbodiimide, and adenylyl imidodiphosphate). The fact that membrane-bound, cold-stable, oligomycin-sensitive ATPase activity is present in poky (with an activity of 1.93 +/- 0.03 mumol/min-mg of protein compared with 1.33 +/- 0.07 mumol/min-mg of protein in the wild-type strain) and also in chloramphenicol-grown wild-type cells suggests that products of mitochondrial protein synthesis play only a limited role in the attachment of the mitochondrial ATPase to the membrane in Neurospora. poky also contains a second form of mitochondrial ATPase, which has an activity of 1.5 +/- 0.2 mumol/min-mg of protein, is oligomycin sensitive but cold labile, and presumably is attached less firmly to the mitochondrial membrane. The two forms, added together, represent a substantial overproduction of mitochondrial ATPase by poky.
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PMID:Mitochondrial adenosine triphosphatase of wild-type and poky Neurospora crassa. 2 38

Transmural nerve stimulation (TNS) with 0.3-msec pulses between 1 and 25 Hz dilated cat cerebral artery segments in the presence of active muscle tone. Maximum vasodilatation occurred at 8 Hz. The dilator response to exogenous acetylcholine, but not to TNS, was abolished by atropine. Neither physostigmine nor hemicholinium affected the dilator response to TNS, which persisted after administration of guanethidine, phenoxybenzamine, propranolol, reserpine, and chronic sympathectomy. However, it was abolished by tetrodotoxin and cold storage. When examined histochemically, cat and rabbit cerebral arteries exhibited a rich plexiform distribution of acetylcholinesterase which was not affected appreciably by sympathetic denervation. These results suggest that vasodilation is not mediated through modification of sympathetic activity. They also indicate the existence of a nonadrenergic, possibly noncholinergic, vasodilator innervation in cat cerebral arteries. Preliminary studies suggest that the transmitter is not histamine, ATP, prostaglandins, gamma-aminobutyric acid, dopamine, or serotonin. The cat cerebral artery segments contrast with the isolated rabbit cerebral arteries which predominantly constrict in response to TNS and show a small dilator response.
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PMID:Neurogenic vasodilation of cat cerebral arteries. 2 5

Nervous tissue pieces from the caudate nucleus and the substantia nigra of the rat were incubated in cold glycerol solutions of decreasing concentrations and then transferred into standard phosphate buffer (pH 7.0) or into tris-K+-Mg++-Ca++ buffer (pH 7.9) containing HMM, prepared from rabbit skeletal muscle by tryptic digestion. As controls, pieces were immersed for an identical period in the same buffers (1) without HMM or (2) with HMM to which had been added 2.5 mM Na+ pyrophosphate or 5 mM ATP. In control neurons smooth-surfaced microfilaments, about 50 A in diameter, were observed. After reaction with HMM, the microfilaments were increased in number and density and in width to 180-200 A. A meshwork was formed. Arrowheads pointing in the same direction were spaced at regular intervals (300-350 A) among short segments of the surfaces of the microfilaments, depending upon the plane of section. More often, however, typical arrowheads were not observed, and the surfaces of the microfilaments were seen coated with polarized side-arms cross-bridging the spaces between adjacent elements at more or less regular intervals. When cross-sectioned, the microfilaments appeared as dense dots from which a material of lesser electron density radiated. Following incubation in HMM solutions containing Na+ pyrophosphate or ATP, no arrowhead structures were seen. Of particular interest was the structural relation of the actin-like filaments with occasional, tapered myosin-like filaments, and with the plasma membrane, which served as anchor points. Mitochondria and smooth ER membranes were observed to be attached to the actin-like filaments or enmeshed in the network. The microtubules, as well as most of the neurofilaments, were disrupted by the glycerination procedure at 4 degrees, and thus no precision about the structural relationship of the actin-like filaments with the latter elements could be added. The role of the actin-like filaments in the transport of material, by a mechanism of chemomechanical transduction, throughout the neuron from sites of synthesis to functional locations, and between several functional locations, is discussed.
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PMID:An ultrastructural study of the microfilaments in rat brain by means of heavy meromyosin labeling. I. The perikaryon, the dendrites and the axon. 5 Jan 39

1) Fast axoplasmic transport in mammalian nerve in vitro was studied using an isotope labeling technique. The rate of outflow in cat sciatic nerve fibers of 410 mm/day in vitro was reduced at temperatures below 38 degrees C with a Q10 of 2.0 in the range 38-18 degrees C and a Q10 of 2.3 at 38-13 degrees C. 2) At a temperature of 11 degrees C a partial failure of transport occurred. At temperatures below 11 degrees C a complete block of fast axoplasmic transport occurred, a phenomenon termed "cold-block." No transport at all was seen over the temperature range of 10-0 degrees C for times lasting up to 48 hr. 3) Transport was resumed after a period of cold-block lasting up to 22 hr when the nerves were brought back to a temperature of 38 degrees C. Some deleterious effects due to cold-block were seen in the recovery phase as indicated by a reduction in crest amplitude, change in its form, and slowed rate. 4) The approximately P level (combined ATP and creatine phosphate) remained near control level in nerves kept at low or cold-block temperatures for times as long as 64 hr. The reduction in fast axoplasmic transport rate seen at low temperatures for times up to 22 hr was therefore considered due to a decrease in the utilization of ATP, a concept in accord with the "transport filament" model proposed to account for fast axoplasmic transport. 5) The sloping of the front of the crest over the temperature range of 18-13 degrees C suggests an additional factor at the lower temperatures. A disassembly of microtubules is discussed as a possible explanation of the cold-block phenomenon.
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PMID:Low temperature slowing and cold-block of fast axoplasmic transport in mammalian nerves in vitro. 5 88


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