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Query: EC:3.6.1.3 (ATPase)
 65,361 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The pH optimum was the same in canine tissue for cardiac and skeletal muscle myosin; when myosin was activated by monovalent cations, the pH optimum was 7.5 while activation of myosin by divalent cations gave a pH optimum of 5.5. Protons were needed for divalent cation activation of myosin. With changes in pH there were concomitant changes in the apparent affinity of enzyme for substrate (S 0.5), such that with a decrease in pH there was an elevation in K+- or NH4+ -activated myosin's apparent affinity for adenosine triphosphate (ATP), and at the same time a decrease in Vmax values of myosin. The converse was true with the divalent cations, Ca++ and Mn++; here with a decrease in pH there was a concomitant decrease in apparent affinity of myosin for ATP, and at the same time an increase in the enzymatic Vmax values. It appeared that hydrogen ions affected the apparent affinity of myosin for substrate and this in turn affected the rate-limiting step in ATPase reaction. Addition of monovalent cations to the divalent cation activating system lowered the activity of myosin, and the converse was true: divalent cations lowered the activity of myosin when activated by monovalent ones in a monovalent cation activating system.
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PMID:Effect of variations in pH on kinetics of myosin. 0 60

An electrochemical potential difference for hydrogen ions ( a protonmotive force) was artifically imposed across the membrane of the anaerobic bacterium Streptococcus lactis. When cells were exposed to the ionophore, valinomycin, the electrical gradient was established by a potassium diffusion potential. A chemical gradient of protons was established by manipulating the transmembrane pH gradient. When the protonmotive force attained a value of 215 mV or greater, net ATP synthesis was catalyzed by the membrane-bound Ca++, Mg++ -stimulated ATPase. This was true whether the protonmotive force was dominated by the membrane potential (negative inside) or the pH gradient (alkaline inside). Under these conditions, ATP synthesis could be blocked by the ATPase inhibitor, dicyclohexylcarbodiimide, or by ionophores which rendered the membrane specifically permeable to protons. These observations provide strong evidence in support of the chemiosmotic hypothesis, which states that the membrane-bound ATPase couples the inward movement of protons to the synthesis of ATP.
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PMID:ATP synthesis driven by a protonmotive force in Streptococcus lactis. 0 50

Proton influx was measured after imposition of an electrochemical potential difference for protons (delta muH+) across the cell membrane of the anaerobe, Streptococcus lactis. As delta muH+ was increased, there was an approximately parallel increase in proton entry, until delta muH+ attained 175 to 200 mV. At this point, a new pathway became available for proton entry, allowing an abrupt increase in both the rate and extent of H+ influx. This gated response depended upon the value of delta muH+ itself, and not upon the value of either the membrane potential or the pH gradient. For delta muH+ above 175 to 200 mV, elevated proton entry occurred only in cells having a functional membrane-bound Ca2+-stimulated, Mg2+stimulated adenosine 5'-triphosphatase (EC 3.6.1.3). When present, elevated proton entry coincided with the appearance of net synthesis of adenosine 5'-triphosphate catalyzed by this adenosine 5'-triphosphatase. These observations demonstrate that membrane-bound adenosine 5'-triphosphatase catalyzes an obligatory coupling between the inward movement of protons and synthesis of adenosine 5'-triphosphate.
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PMID:Obligatory coupling between proton entry and the synthesis of adenosine 5'-triphosphate in Streptococcus lactis. 2 Nov 65

Proton translocating ATPase of oxidative phosphorylation was divided into three functional units: pump, channel, and gate. This was achieved by the use of highly stable pure ATPase obtained from a thermophilic bacterium PS3. The pump and gate were found in a catalytic moiety of the ATPase called TF1, and the channel was in the remaining hydrophobic moiety of the ATPase called TF0 which rendered TF1 sensitive to energy transfer inhibitor such as DCCD. TF1 was composed of five subunits (alpha, 56,000; beta, 53,000; gamma, 32,000; delta, 15,500; epsilon, 11,000 daltons). The essential component of the pump was beta-subunit, since beta gamma-complex or alpha beta delta-complex showed ATPase activity. The gate which blocked passive leakage of protons through TF0 in the proteoliposomes was shown to be gamma delta epsilon-complex in TF1. Both delta- and epsilon-subunits were required to connect alpha beta gamma-complex to TF0. TF0 was identical to the channel and was composed of three kinds of subunits (19,000, 13,500, and 5,400 daltons) and the smallest one was [14C]-DCCD binding protein. When the ATPase was incorporated into vesicles containing highly stable saturated branched phospholipids, ATP-driven electrochemical potential of proton (delta mu H+ = 253mV) and proton gradient driven net synthesis of ATP were demonstrated. For these activities, pump, channel, and gate of proton translocating ATPase were all required.
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PMID:Proton translocating ATPase: its pump, gate, and channel. 2 68

The phospholipid and fatty acid composition and role of phospholipids in enzyme and transport function of gastric (H+ + K+)-ATPase vesicles was studied using phospholipase A2 (bee venom). The composition (%) was phosphatidyl-choline (PC) 33%; sphingomyelin (sph) 25%; phosphatidylethanolamine (PE) 22%; phosphatidylserine (PS) 11%; and phosphatidylinositol (PI) 8%. The fatty acid composition showed a high degree of unsaturation. In both fresh and lyophilized preparations, even with prolonged incubation, only 50% of phospholipids were hydrolyzed, but the amount of PE and PS disappearing was increased following lyophilization. There was a marked decrease in K+-ATPase activity (75%) but essentially no loss of the associated K+ p-nitrophenyl phosphatase was found. ATPase activity could be largely restored by various phospholipids (PE greater than PC greater than PS). There was also an increase in Mg2+-ATPase activity, partially reversed in fresh preparations by the addition of phospholipids (PE greater than PS greater than PC). Proton transport activity of the preparation was rapidly inhibited, initially due to a large increase in the HCl permeability of the preparation. Associated with these enzymatic and functional changes, the ATP-induced conformational changes, as indicated by circular dichroism spectra were inhibited.
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PMID:Effect of phospholipase A2 on purified gastric vesicles. 4 34

Transverse cryostat sections of skeletal muscle were fixed in a solution containing 1.5% glutaraldehyde and 1.5% sulfosalicylic acid and stained in a solution containing equal volumes of 3% hydrogen peroxide and 50% ethanol saturated with o-tolidine. Myoglobin in the sarcoplasm of muscle fibers was precipitated and stained blue. Applicability of this method to cryostat sections, without glutaraldehyde fixations prior to freezing, allowed the myoglobin content of individual muscle fibers to be correlated with other histochemical characteristics of the same fibers seen in serial sections. In the dark red bovine sternomandibularis muscle, fibers with weak adenosine triphosphatase (ATPase) and strong succinate dehydrogenase (SDH) activity always exhibited strong myoglobin staining. An equal degree of staining was found in many fibers with strong ATPase and intermediate to strong SDH activity. Fibers with strong ATPase and weak SDH activity were less strongly stained than the preceding types.
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PMID:A method for myoglobin in cryostat sections of muscle by precipitation with sulfosalicylic acid. 9 25

The demonstrated role of proton translocation and resulting electrochemical activity gradients (protonmotive force) in ATP synthesis by chloroplasts is noted. Evidence for the participation of conformational changes in the terminal ATPase (coupling factor, or CF1) is reviewed. Hydrogen exchange into ordinarily cyptic groups of the molecule occurs only when the subtending membranes are put under the stress of a protonmotive force. Since up to 100 hydrogen atoms per mole are involved in the energy-dependent exchange the conformational change permitting tham access to the medium must be a major one. Chemical reagents are beginning to be used to attack groups on CF1 that are exposed only when the membranes are energized. N-ethylmaleimide binds covalently, sulfate causes as yet unspecified damage, and permanganate leads to oxidative damage to CF1 under energized conditions. The last two reagents are analogues of phosphate, and ADP must be added for them to inhibit. On the basis of this and other differences between the conditions needed for inhibition by permanganate or sulfate, and that by N-ethylmaleimide or the hydrogen exchange, a somewhat complex scheme involving several successive or alternative conformations of CF1 can be postulated. Questions are raised as to the way in which a conformational change in a bound protein could be caused by a proton activity gradient across its supporting membrane, and as to whether the altered conformations might constitute a part of the energy transformations leading to ATP synthesis.
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PMID:Chloroplast membranes and coupling factor conformations. 12 71

A particulate subcellular fraction from Escherichia coli K-12 induced in anaerobic sn-glycerol 3-phosphate (G3P) dehydrogenase and fumarate reductase can catalyze under anaerobic conditions the transfer of hydrogens from G3P to fumarate, with attendant generation of high-energy phosphate. The phsophorylation process is more sensitive than the transhydrogenation process to inhibition by the detergent Triton X-100. The same is true with respect to sensitivity to sodium azide, carbonyl cyanide m-chlorophenylhydrazone and N,N'-dicyclohexylcarbodiimide. Such a preparation derived from cells with beta-galactoside permease can accumulate thiomethyl beta-D-galactoside anaerobically, and the accumulation can be stimulated twofold by adding G3P and fumarate. Mutants lacking the membrane-associated Mg2+-dependent adenosine triphosphatase cannot grow anaerobically on glycerol with fumarate as the hydrogen acceptor, although they can grow aerobically on glycerol alone.
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PMID:Anaerobic energy-yielding reaction associated with transhydrogenation from glycerol 3-phosphate to fumarate by an Escherichia coli system. 12 85

Several cardiotonic steroids have been modified by reduction of the unsaturated lactone and their interactions with the sodium- and potassium-activated ATPase ((Na+ + K+)-ATPase) have been investigated. Reduction of the unsaturated lactone results in a decrease in binding affinity due primarily to an increase in the dissociation rate constant concomitant with a decrease in the activation free energy of dissociation. This decrease in activation free energy is about 2 to 4 kcal, which is approximately equal to the energy of one hydrogen bond. It is suggested that the increase in dissociation rate due to reduction of the unsaturated lactone may make possible the use of these compounds as affinity ligands for purification of the (Na+ + K+)-ATPase or an ouabain-binding fragment.
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PMID:Increase in dissociation rate constants of cardiotonic steroid-brain (Na+ + K+)-ATPase complexes by reduction of the unsaturated lactone. 12 94

Oral heavy water (D20) administration and enzymatic changes were studied in rat testis. D20 caused marked gradual decrease in the weight of the body as well as the testes throughout the treatment interval ranging from 1 to 6 weeks. Following D20 oral administration, an overall marked fall in the activity of acid phosphatase and glucose-6-phosphatase was seen. However,, the activity of lactic and succinic dehydrogenases, alkaline posphatase, and adenosine triphosphatase increased following treatment. These results suggest on altered metabolism of the testes in response to D20 administration and corroborate the view that biological systems do discriminate between hydrogen and deuterium.
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PMID:Oral D2O administration and enzymatic changes in rat testis. 13 64


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