Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: HUMANGGP:021133 (ATP)
 132,114 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

1. Based on incorporation of radioactively labeled N-ethylmaleimide, the readily reactive thiol groups of isolated myosin (EC 3.6.1.3) from fast, slow and cardiac muscles could be classified into 3 types. All 3 myosins contain 2 thiol-1, 2 thiol-2 and a variable number of thiol-3 groups per molecule. Both thiol-1 and thiol-2 groups which are essential for functioning of the K+-stimulated ATPase, are located in the heavy chains in all 3 myosin types. 2. The variation in the incorporation pattern of N-ethylmaleimide over the 3 thiol group classes under steady-state conditions of Mg(2+) - ATP hydrolysis allowed different conformations of some reaction intermediates to be characterized. In all 3 types of myosin the hydrolytic cycle of Mg(2+) - ATP was found to be controlled by the same step at 25 degrees C. In all three cases, this rate-limiting step is changed in the same way by lowereing temperature. 3. Using the chemically determined molecular weights for myosin light chains, their stoichiometry was found on the basis of sodium dodecyl sulfate electrophoresis to be 1.2 : 2.1 : 0.8 for light chain-1: light chain-2:light chain-3 per molecule of fast myosin, 2.0 : 1.9 for light chain-1:light chain-2 per molecule of slow myosin and 1.9 : 1.9 for light chain-1:light chain-2 per molecule of cardiac myosin. This qualitative difference in light subunit composition between the fast and the two types of slow myosin is not reflected in the small variations of the characteristics exhibited by the isolated myosins, but rather seems to be connected with their respective myofibrillar ATPase activities.
 ...
PMID:Radioactive labeling and location of specific thiol groups in myosin from fast, slow and cardiac muscles. 0 73

TTP accelerated ATP-induced superprecipitation of actomyosin in as low a concentration as 30 muM and decreased light scattering by actomyosin. These effects could also be observed in the same way, but to a lesser degree, by addition to TDP. Myosin was able to hydrolyze TTP to TDP, but some important differences were confirmed between myosin TTPase and ATPase. Myosin TTPase was inhibited by actin and showed a much larger Km than that of ATPase. TTP significantly inhibited myosin B ATPase and ATP greatly inhibited myosin B TTPase. These findings suggest that the accelerating effect of TDP and TTP may be due to the binding of thiamine phosphate to the regulatory site of myosin followed by a change in its physical chemical property, rather than due to the competitive binding of thiamine phosphate to the catalytically activity site of myosin.
 ...
PMID:Thiamine triphosphatase activity of myosin and accelerating effect of thiamine di- and tri-phosphates on superprecipitation of actomyosin. 0 81

The role of calcium and magnesium-ATP on the structure and contractility in motile extracts of Amoeba proteus and plasmalemma-ectoplasm "ghosts" of Chaos carolinensis has been investigated by correlating light and electron microscope observations with turbidity and birefringence measurements. The extract is nonmotile and contains very few F-actin filaments and myosin aggregates when prepared in the presence of both low calcium ion and ATP concentrations at an ionic strength of I = 0.05, pH 6.8. The addition of 1.0 mM magnesium chloride, 1.0 mM ATP, in the presence of a low calcium ion concentration (relaxation solution) induced the formation of some fibrous bundles of actin without contracting, whereas the addition of a micromolar concentration of calcium in addition to 1.0 mM magnesium-ATP (contraction solution) (Taylor, D. L., J. S. Condeelis, P. L. Moore, and R. D. Allen. 1973. J. Cell Biol. 59:378-394) initiated the formation of large arrays of F-actin filaments followed by contractions. Furthermore, plasmalemma-ectoplasm ghosts prepared in the relaxation solution exhibited very few straight F-actin filaments and myosin aggregates. In contrast, plasmalemmaectoplasm ghosts treated with the contraction solution contained many straight F-actin filaments and myosin aggregates. The increase in the structure of ameba cytoplasm at the endoplasm-ectoplasm interface can be explained by a combination of the transformation of actin from a less filamentous to a more structured filamentous state possibly involving the cross-linking of actin to form fibrillar arrays (see above-mentioned reference) followed by contractions of the actin and myosin along an undetermined distance of the endoplasm and/or ectoplasm.
 ...
PMID:The contractile basis of ameboid movement. II. Structure and contractility of motile extracts and plasmalemma-ectoplasm ghosts. 0 80

Reconstituted actomyosin (ATP phosphohydrolase, EC 3.6.1.3) (0.400 mg F-actin/mg myosin) in 10.0 muM ATP loses 96% of its specific ATPase activity when its reaction concentration is decreased from 42.0 mug/ml down to 0.700 mug/ml. The loss of specific activity at the very low enzyme concentrations is prevented by the addition of more F-actin to 17.6 mug/ml. It is concluded that at low actomyosin concentrations the complex dissociates into free myosin with a very low specific ATPase activity and free F-actin with no ATPase. The dissociation of the essential low molecular weight subunits of myosin from the heavy chains at very low actomyosin concentrations may be a contributing factor. Actomyosin has its maximum specific activity at pH 7.8-8.2. The Km for ATP is 9.4 muM, which is at least 20-fold greater than myosin's Km for ATP. The actin-activated ATPase of myosin follows hyperbolic kinetics with varying F-actin concentrations. The Km values for F-actin are 0.110 muM (4.95 mug/ml) at pH 7.4 and 0.241 muM (10.8 mug/ml) at pH 7.8. The actin-activated maximum turnover numbers for myosin are 9.3 s-1 at pH 7.4 and 11.6 s-1 at pH 7.8. The actomyosin ATPase is inhibited by KCl. This KCl inhibition is not competitive with respect to F-actin, and it is not a simple form of non-competitive inhibition.
 ...
PMID:Steady-state studies of the actin-activated adenosine triphosphatase activity of myosin. 0 39

Cardiac myosin from thyrotoxic animals (myosin-T) exhibits elevated Ca2+ -ATPase activity which is resistant to further stimulation by sulfhydryl modification. In the present study, we have compared the enzymatic properties of myosin-T with those of myosin from euthyroid rabbits (myosin-N) and the derivatives of myosin-T and myosin-N formed by blocking the most rapidly reacting class of thiols (SH1) with N-ethylmaleimide (NEM). Vmax for Ca2+ -ATPase of myosin-T was about 250% greater than myosin-N and was nearly the same as NEM-modified myosin-N. Values for the apparent Km of myosin-T and NEM-modified myosin-N were 200% greater than the value for unmodified myosin-N. Vmax and Km for K+ (EDTA)-ATPase activity of NEM-modified myosin-T and myosin-N were identical. The Ca2+ saturation, pH, and salt-dependency curves for the ATPase activity of myosin-T were parallel to the curves for myosin-N and differed from those for the NEM-modified myosins. Myosin-T exhibited an increased rate of hydrolysis of ATP, CTP, and UTP in both low (0.05m) and high (0.5m) KCl medium. NEM-modified myosin-N showed increased hydrolysis of ATP and CTP in low KCl medium and increased hydrolysis of ATP, CTP, and UTP in high KCl medium. These results support the hypothesis that the enzymatic behavior of myosin-T may be caused by an alteration in the active site near the SH, thiols. The unique enzymatic properties of myosin-T did not seem to be the result of a major change in structure. The electrophoretic pattern of light chains from myosin-T and myosin-N was the same in polyacrylamide gels containing either 8 M urea at pH 8.6 or sodium dodecyl sulfate. Also, myosin-T had a normal amino acid composition and lacked 3-methyl-histidine and hot acid-stable phosphate.
 ...
PMID:Enzymatic properties of native and N-ethylmaleimide-modified cardiac myosin from normal and thyrotoxic rabbits. 0 19

The flexibility of the tertiary structure around the active site of myosin ATPase [EC 3.6.1.3] was studied using the reactivity of two specific thiol groups, S1 and S2, as a structural probe. The following four maleimide derivatives were used as thiol-directed reagents: N-ethylmaleimide (NEM), N-(4-methoxy-2-benzimidazolyl methyl) maleimide (MBM), N-(p-(2-benzimidazolyl)phenyl)maleimide (BIPM) and N-(4-dimethyl-amino-3,5-dinitrophenyl)maleimide (DDPM). 1. All the maleimide derivatives used activated the Ca2+-ATPase activity and inhibited the EDTA-ATPase activity, like NEM, indicating that they modified S1. The rate of modification of S1 by NEM and BIPM increased with increasing pH, while that by DDPM decreased. BIPM simultaneously modified S1 and S2. 2. S1 showed much higher reactivity toward the maleimides, except for BIPM, than did N-acetylcysteine (N-Ac-Cys) a low molecular-weight model compound. The extremely small pKa value of S1, 6.28, accounted for this high reactivity. In addition, the ATP-induced increase in its reactivity inducated that S1 was in a buried state. Kinetic analysis showed that the teritiary structure around S1 at alkaline pH differed from that at acidic pH. 3. The apparent rate constant of S2-modification with NEM was approximately one seven-hundredth and one four-hundredth of those of S1 and N-Ac-Cys, respectively. Fluorimetric studies using BIPM revealed that S2 in the buried state was exposed upon adding ATP; this was compensated by the burying of some other thiol group(s) (Sp). Non-linearity of the Arrhenius plots of the reaction rate of S2 suggested that the S2 region of myosin had different conformations at high and low temperatures, the transition temperature being 10--15degrees. This non-linearity completely disappeared in the presence of Mg2+-ATP. On the other hand, Arrhenius plots for the thiols reactive to BIPM did not show non-linearity in the presence or absence of ATP.
 ...
PMID:Thiols of myosin. IV. "Abnormal" reactivity of S1 thiol and the conformational changes around S2 thiol. 0 75

The brush border of intestinal epithelial cells consists of an array of tightly packed microvilli. Within each microvillus is a bundle of 20-30 actin filaments. The basal ends of the filament bundles are embedded in and interconected by a filamentous meshwork, the terminal web, which lies directly beneath the microvilli. When calcium and ATP are added to isolated brush borders that have been treated with the detergent, Triton X-100, the microvillar filament bundles rapidly retract into and through the terminal web region. Biochemical studies of brush border contractile proteins suggest that the observed microvillar contraction is actomyosin mediated. We have shown previously that the major protein of the brush border's actin (Tilney, L. G., and M. S. Mooseker. 1971. Proc. Natl. Acad. Sci. U. S. A. 68:2611-2615). The brush border also contains a protein with the same molecular weight as the heavy chain subunit of myosin (200, 000 daltons). In addition, preparations of demembranated brush borders exhibit potassium-EDTA ATPase activity of 0.02 mumol phosphate/mg-min (22 degrees C); this assay is diagnostic for myosin-like ATPase isolated from vertebrate sources. Other proteins of the brush border include a 30,000 dalton protein with properties similar to those of tropomyosin, and a protein with the same molecular weight as the Z band protein, alpha-actinin (95,000 daltons). How these observations bear on the basis for microvillar movements in vivo is discussed within the framework of our recent model for the organization of actin and myosin in the brush border (Mooseker, M. S., and L. G. Tilney. 1975. J. Cell Biol. 67:725-743).
 ...
PMID:Brush border motility. Microvillar contraction in triton-treated brush borders isolated from intestinal epithelium. 1 Dec 22

The increase in temperature leads to a decrease in pKa of the group responsible for the activation of CaATP2- hydrolysis by myosin in the alkaline zone of pH. At 20-25 degrees the pKa value is about 9. The value of ionization heat (deltaHi) calculated from pKa temperature dependence is 7.6+/-+/-0.8 kcal/mol. These values are approximated to the values known for phenol hydroxyl of tyrosine. It has been demonstrated that the acceleration of CaATP2- hydrolysis at alkaline values of pH is accompanied by an increase in the Arrhenius energy of activation (Ea), determined from the temperature dependence of the maximal reaction rate (V). The increase of Ea at alkaline values of pH is apparent and is due to an increase in the concentration of a deprotonized form of the enzyme, having a higher activity. A comparison of activation parameters of the reaction at alkaline and neutral values of pH permits to conclude that the acceleration of CaATP2- hydrolysis at alkaline values of pH is due to the acceleration of the limiting step of the reaction. It has also been found that at alkaline values of pH the power of myosin binding with ADP, a competitive inhibitor and the reaction product, is decreased. It is assumed that the acceleration of ATP hydrolysis at alkaline values of pH is due to accelerated dissociation of the reaction products from the active centre of the enzyme, as a result of ionization of a functional group of myosin, probably of the tyrosine residue.
 ...
PMID:[Alkaline activation of myosin ATPase: some thermodynamic characteristics]. 1 35

I-protein inhibited theMg-activated ATPase [EC 3.6.1.3] activity of actinomyosin by approximately 50% at low ionic strength. Concomitantly, the onset of superprecipitation was retarded. I-protein was found to bind to myosin, but not to F-actin. The inhibitory action of I-protein occurred only in the absence of Ca ions in the troponintropomyosin-actin myosin system. Addition of Ca ions abolished the effect. Thus, it is very likely that I-protein prevents unnecessary hydrolysis of ATP in the relaxed state of muscle.
 ...
PMID:I-protein, a new regulatory protein from vertebrate skeletal muscle. III. Function. 1 32

The changes in birefringence in the rigor to relax transition of single triton-extracted rabbit psoas muscle fibers have been investigated with quantitative polarized light techniques. The total birefringence of rest lenght fibers in rigor was (1.46 +/- 0.08) x 10(-3) and increased to (1.67 +/- 0.05) x 10(-3) after Mg-ATP relaxation. Pyrophosphate relaxation increased the total birefringence only slightly, whereas subsequent Mg-ATP relaxation elicited the maximum increase in birefringence. Changes in lattice spacing did not account for the total increase in birefrigence during relaxation. Moreover, the increase in total birefringence was attributable to increases in intrinsic birefringence as well as form birefringence. No change in birefringence was exhibited upon exposure to a relaxation solution after myosin extraction. Synthetic myosin filaments were prepared and treated with relaxation and rigor solutions. The negatively stained filaments treated with a rigor solution had gross irregular projections at either end, while the filaments treated with a relaxing solution were more spindle shaped. The results are compatible with the view that the subfragment-2 moieties of myosin angle away from the myosin aggregates (light meromyosin) to permit the attachment of the subfragment-1 moieties to actin.
 ...
PMID:Quantitative studies on the polarization optical properties of striated muscle. I. Birefringence changes of rabbit psoas muscle in the transition from rigor to relaxed state. 1 16


1 2 3 4 5 6 7 8 9 10 Next >>