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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)

Stable membrane proteins and lipids are convenient to study biomembranes. Two stable proton translocating proteins were purified and reconstituted into vesicles capable of proton translocation. One was a thermostable ATPase (TF0-F1) of thermophilic bacterium PS3 and the other was rhodopsin of Halobacterium halobium. TF0-F1 was composed of a proton pump moiety (TF1) and a proton channel moiety (TF0). TF1 was the first membrane ATPase which was crystallized and reconstituted from its five polypeptides. Like TF0 and TF1, the rhodopsin in purple membrane was highly stable against dissociating agents, acids and alkali. Phospholipids of these biomembranes were also stable and contained no unsaturated fatty acyl groups. The molecular species of the phospholipids of PS3 were determined by mass chromatography. Measurements were made of the difference in electrochemical potential of protons (deltamicronH+) across the membrane of the reconstituted vesicles. The deltamicronH+ attained was 312 mV in TF0-F1 vesciles and was 230 mV in the rhodopsin vesicles. To conclude that electron transport components are not necessary for ATP synthesis in energy yielding biomembranes, two experiments were performed: The ATP synthesis was observed i) on acid-base treatment of TF0-F1 vesicles, and ii) on illumination of the rhodopsin-TF0-F1 vesicles.
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PMID:Proton translocation by ATPase and bacteriorhodopsin. 1 75

There is evidence that membrane proteins can serve as the functional units of ionic transport in biological membranes. Laser Raman spectroscopy has been used to probe specific molecular interactions inside two models of transport membrane proteins, valinomycin and gramicidin A. Conformational changes of these molecules, as well as specific interactions with ions, can be detected and may help elucidate how membrane transport proteins such as Na+ minus K+ ATPase and rhodopsin function. Resonance Raman spectroscopy has also been used to study conformational changes and protein-chromophore interactions in rhodopsin, the membrane protein that acts as the primary unit of visual excitation in the eye.
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PMID:Models of ionic transport in biological membranes. Raman spectroscopy as a probe of valinomycin, gramicidin A', and rhodopsin conformations. 4 37

Na+, K+-ATPase and Mg++-ATPase are shown to be distributed non-uniformely in different subfractions of the rod outer segments (ROS) of bovine retina. Distribution of the enzymes differs significantly from that of rhodopsin. Predominant portion of Na+, K+-ATPase and Mg++-ATPase is concentrated within the subfractions with the lowest rhodopsin content. The most purified subfractions ROS containing the main amount of rhodopsin lack Na+, K+-ATPase at all, the activity of Mg++-ATPase does not exceed 0,4 plus or minus 0,05 mumoles Pi/mg protein-hour. Distribution of the succinic dehydrogenase is similar to this Na+, K+-ATPase. The data show that Na+, K+-ATPase activity in the ROS fraction is due to the contamination by the inner segment membranes, and that this enzyme is absent in the photoreceptive membranes of ROS.
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PMID:[Distribution of Na+, K+-ATPase and Mg+-ATPase in different subfractions of rod outer segments]. 12 90

Highly purified fraction of squid photoreceptor membranes exhibits relatively low activity of Na+,K+-ATPase. No correlation was observed between the distribution of rhodopsin and Na+,K+-ATPase activity among photoreceptor membrane subfractions obtained from rhabdomeres. On the basis of these data, it is suggested that Na+,K+-ATPase and rhodopsin are localized in different membrane structures. In most purified fractions of rhabdomeres, the ratio of rhodopsin to total protein amounted up to 45--50%. In Triton X-100 extracts from membrane fractions, significant enrichment in rhodopsin content was observed.
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PMID:[Rhabdomere adenosine triphosphatase systems of the squid Todarodes sloanei pacificus]. 13 81

1H nuclear magnetic resonance techniques were used to study the binding of uridine 5'-triphosphate to the Ca2+-transport ATPase (EC 3.6.1.3) of sarcoplasmic reticulum vesicles from rabbit skeletal muscle. The nuclear spin relaxation times determined for the bound nucleotide are used to characterize the rotational motion of the ATPase to which the nucleotide is bound. The results, assuming an anisotropic model for the motion of the ATPase in the membrane, place a low upper limit on the rotational correlation time of the ATPase. This indicates that the motion of the ATPase in the membrane is quite rapid when compared, for example, with the motion found for other membrane-bound proteins such as rhodopsin.
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PMID:Rapid anisotropic motion of the Ca2+-transport ATPase of the rabbit skeletal muscle sarcoplasmic reticulum. 14 71

Electroretinographic (ERG), morphometric and biochemical studies on retinas from monkeys or rats reveal that moderate level developmental lead (Pb) exposure produces long-term selective rod deficits and degeneration. The present studies determined whether similar alterations occur following low level developmental Pb exposure. Long-Evans rats, exposed to Pb only via dam's milk from parturition to weaning, had mean blood Pb of 18.8 micrograms/dl at weaning and 6.6 micrograms/dl at 90 days of age. Morphometric and ultrastructural studies revealed no signs of rod loss or degeneration although the presence of glycogen in some rod mitochondria suggests the occurrence of a metabolic dysfunction. Retinal sensitivity and rhodopsin content per eye were decreased in a manner such that, they followed the established log-linear relationship. A- and b-wave voltage- and latency-log intensity functions, generated from single-flash ERGs in fully dark-adapted rats, revealed that low level Pb exposure caused a 25% and 15% decrease in mean amplitude, a 0.5 and a 0.5 log unit decrease in absolute sensitivity, and a 23% and 16% increase in mean latency, respectively. Scotopic (rod-mediated) and photopic (cone-mediated) flicker fusion frequency measures revealed selective rod deficits. Adult rats had a 15% inhibition of retinal cGMP-phosphodiesterase resulting in a 19% and 12% increase in cGMP in dark- and light-adapted states, respectively. The above data confirm and extend our previous studies conducted in rats with blood lead levels of 59 micrograms/dl during development. The rhodopsin and cyclic nucleotide metabolism data, as well as our recent data showing an inhibition of retinal Na+, K(+)-ATPase, are entirely consistent with the observed ERG changes. The fact that rat rods are similar to monkey and human rods suggests the relevance and applicability of these data to low level pediatric Pb poisoning. Thus, these data suggest that alterations in rod sensitivity and temporal processing may occur in children exposed to low levels of lead during perinatal development.
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PMID:Low level developmental lead exposure decreases the sensitivity, amplitude and temporal resolution of rods. 166 51

The role of 48-kDa protein in visual transduction remains unresolved. Two hypotheses for its role in quenching the light activation of cyclic GMP cascade suggest that the protein binds to either phosphodiesterase or phosphorylated rhodopsin. Since the protein is also reported to bind ATP, we anticipated that the protein may have ATP hydrolyzing activity, and in analogy with the GTP-binding protein of the rod outer segments, such activity may be greatly enhanced by the elements of transduction cyclic GMP cascade, permitting the protein to function cyclically as GTP-binding protein does. We found that purified 48-kDa protein hydrolyzes ATP but at a slow rate of 0.04-0.05 per min. The Km for ATP is about 45-65 microM. The activity is inhibited noncompetitively by ADP with a Ki of about 50 microM. The ATPase activity of 48-kDa protein is not affected by rhodopsin, bleached rhodopsin, phosphorylated rhodopsin, unactivated cyclic GMP phosphodiesterase, or phosphodiesterase (PDE) activated by GMP PNP-bound G-protein. These data show that although 48-kDa protein has ATPase activity, lack of regulation of this activity by the elements of visual transduction makes it unlikely for this activity to have a role in quenching the light activation of cyclic GMP cascade.
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PMID:Photoreceptor rod outer segment 48-kDa protein has ATPase activity. 215 Jul 55

The rotational dynamics of the purified dicyclohexylcarbodiimide-sensitive H(+)-ATPase (DSA) reconstituted into phospholipid vesicles and of the DSA coreconstituted with the proton pump bacterio-rhodopsin were examined by using the technique of time-resolved phosphorescence emission anisotrophy. The phosphorescent probe erythrosin isothiocyanate was used to covalently label the gamma-polypeptide of DSA before reconstitution. Rotational correlation times were measured under a variety of conditions. The rotational correlation time was independent of the viscosity of the external medium but increased significantly as the microviscosity of the membrane increased. This indicates the rotational correlation times are a measure of the enzyme motion within the membrane. The activation energy associated with the rotational correlation time is 8-10 kcal/mol. At 4 degrees C, the correlation time, typically approximately 100-180 microseconds, was unaffected by the addition of substrates and the presence of a membrane pH gradient. Therefore, molecular rotation of the DSA does not appear to play an important role in enzyme catalysis or ion pumping.
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PMID:Rotational dynamics of chloroplast ATP synthase in phospholipid vesicles. 215 33

Rhodopsin is a member of a family of receptors that contain seven transmembrane helices and are coupled to G proteins. The nature of the interactions between rhodopsin mutants and the G protein, transduction (Gt), was investigated by flash photolysis in order to monitor directly Gt binding and dissociation. Three mutant opsins with alterations in their cytoplasmic loops bound 11-cis-retinal to yield pigments with native rhodopsin absorption spectra, but they failed to stimulate the guanosine triphosphatase activity of Gt. The opsin mutations included reversal of a charged pair conserved in all G protein-coupled receptors at the cytoplasmic border of the third transmembrane helix (mutant CD1), replacement of 13 amino acids in the second cytoplasmic loop (mutant CD2), and deletion of 13 amino acids from the third cytoplasmic loop (mutant EF1). Whereas mutant CD1 failed to bind Gt, mutants CD2 and EF1 showed normal Gt binding but failed to release Gt in the presence of guanosine triphosphate. Therefore, it appears that at least the second and third cytoplasmic loops of rhodopsin are required for activation of bound Gt.
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PMID:Rhodopsin mutants that bind but fail to activate transducin. 221 4

ATP can cause dramatic structural changes in the outer segment of rod photoreceptors. These changes can be visualized by means of a concomitant light-scattering signal AD, a decrease in scattered light intensity of over 20%. The large size of the signal suggests that major structural changes occur. The underlying molecular events may reflect an important, yet still unknown, part of the photoreceptor machinery. AD signals reflect ATPase-driven transmembrane events which occur in and at the disk membrane. Their only structural prerequisite is the structural integrity of the disk compartment. The angular dependence of AD, which can be mimicked by an osmotically-induced disk-swelling, suggests that the disk compartment swells during the production of the AD signal. AD signals proceed with first-order kinetics (half-life = 1 min at 20 degrees C and ATP concentrations of greater than 100 microM) and are accompanied by the hydrolysis of approximately 4 mol ATP (mol rhodopsin)-1. The AD signal is inhibited by a number of transport ATPase inhibitors (quercetin, NBD.Cl, vanadate, DCCD), but not by oligomycin, azide and ouabain. The sensitivity to DCCD, together with the fact that except magnesium no other cation has to be present, points to a proton translocation. This proton transport appears to be electrogenic, since AD signals require the presence of a permeant anion. In physiological saline this is chloride, and the chloride flux is facilitated by a DIDS-sensitive anion transport unit in the disk membrane.
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PMID:Optical probes of intradiskal processes in rod photoreceptors. I: Light-scattering study of ATP-dependent dark reactions. 252 60


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