scholarly journals The reversibility of adenosine triphosphate cleavage by myosin

1973 ◽  
Vol 133 (2) ◽  
pp. 323-328 ◽  
Author(s):  
C. R. Bagshaw ◽  
D. R. Trentham
Keyword(s):  
Muscle Contraction ◽  
Active Site ◽  
Energy Exchange ◽  
Atp Hydrolysis ◽  
Mechanical Energy ◽  
Standard Free Energy ◽  
Standard Free Energy Change ◽  
Heavy Meromyosin ◽  
Cleavage Step ◽  
Hydrolysis Of

For the simplest kinetic model the reverse rate constants (k−1 and k−2) associated with ATP binding and cleavage on purified heavy meromyosin and heavy meromyosin subfragment 1 from rabbit skeletal muscle in the presence of 5mm-MgCl2, 50mm-KCl and 20mm-Tris–HCl buffer at pH8.0 and 22°C are: k−1<0.02s−1 and k−1=16s−1. Apparently, higher values of k−1 and k−2 are found with less-purified protein preparations. The values of k−1 and k−2 satisfy conditions required by previous 18O-incorporation studies of H218O into the Pi moiety on ATP hydrolysis and suggest that the cleavage step does involve hydrolysis of ATP or formation of an adduct between ATP and water. The equilibrium constant for the cleavage step at the myosin active site is 9. If the cycle of events during muscle contraction is described by the model proposed by Lymn & Taylor (1971), the fact that there is only a small negative standard free-energy change for the cleavage step is advantageous for efficient chemical to mechanical energy exchange during muscle contraction.

Inhibition of the Ecto-ATPdiphosphohydrolase of Schistosoma mansoni by Thapsigargin

2000 ◽  
Vol 20 (5) ◽  
pp. 369-381 ◽  
Author(s):  
Samantha M. Martins ◽  
Christiane R. Torres ◽  
Sérgio T. Ferreira
Keyword(s):  
Schistosoma Mansoni ◽  
Active Site ◽  
Calcium Transport ◽  
Atp Hydrolysis ◽  
External Surface ◽  
Specific Inhibitor ◽  
Etiologic Agent ◽  
Endoplasmic Reticulum Calcium ◽  
P Type ◽  
Hydrolysis Of

ATPdiphosphohydrolases (ATPDases) are ubiquitous enzymes capable ofhydrolyzing nucleoside di- and triphosphates. Although a number ofpossible physiological roles have been proposed for ATPDases, detailedstudies on structure-function relationships have generally been hamperedby the lack of specific inhibitors of these enzymes. We have previouslycharacterized a Ca2+-activated ATPDase on the external surface ofthe tegument of Schistosoma mansoni, the etiologic agent of humanschistosomiasis. In the present work, we have examined the effectsof thapsigargin, a sesquiterpene lactone known as a high affinityinhibitor of sarco-endoplasmic reticulum calcium transport (SERCA)ATPase, on ATPDase activity. Whereas other lactones tested had littleor no inhibitory action, thapsigargin inhibited ATP hydrolysis by the ATPDase (Ki∼20 μM). Interestingly, hydrolysis of ADP was notinhibited by thapsigargin. The lack of inhibition of ATPase activityby orthovanadate, a specific inhibitor of P-type ATPases, and theinhibition of the Mg2+-stimulated ATP hydrolysis by thapsigarginruled out the possibility that the observed inhibition of the ATPDaseby thapsigargin could be due to the presence of contaminating SERCAATPases in our preparation. Kinetic analysis indicated that a singleactive site in the ATPDase is responsible for hydrolysis of both ATPand ADP. Thapsigargin caused changes in both Vmax and Km for ATP, indicating a mixed type of inhibition. Inhibition by thapsigarginwas little or not affected by changes in free Ca2+ or Mg2+concentrations. These results suggest that interaction of thapsigarginwith the S. mansoni ATPDase prevents binding of ATP or its hydrolysisat the active site, while ADP can still undergo catalysis.

ATP-Dependent Synthetases and Ligases

2007 ◽  
Author(s):  
Perry A. Frey ◽  
Adrian D. Hegeman
Keyword(s):  
Free Energy ◽  
Ethyl Acetate ◽  
Reaction Mechanisms ◽  
Standard Free Energy ◽  
Free Energy Change ◽  
Energy Change ◽  
Free Energy Barrier ◽  
Standard Free Energy Change ◽  
Face To Face ◽  
Hydrolysis Of

The joining of two molecules is energetically unfavorable in an aqueous medium when the substrates correspond to hydrolysis products. In biochemistry, such ligations are driven by the free energy released by the hydrolysis of MgATP or an energetically equivalent molecule. The ATP-dependent synthetases and ligases catalyze reactions in which water is extracted from two molecules that become joined. The amount of free energy available depends on the site at which the ATP molecule is cleaved. The most common cleavage modes and the free energy change under standard conditions, which are pH = 7.0, 25°C, and 1 mM free Mg2+, are given in (Alberty, 1994; Arabshahi and Frey, 1995). Hydrolysis of the α,β-phosphoanhydride linkage to form AMP and PPi releases 3.2 kcal mol–1 more free energy than hydrolysis of the β,γ-linkage. In the actions of ATP-dependent ligases and synthetases, the free energy released in the hydrolysis of MgATP is used to overcome the energetic barrier to the elimination of water. The general principle is exemplified by the free energy barrier for the formation of ethyl acetate from acetate and ethanol under standard conditions, which is ΔG' = +4 kcal mol−1 (Jencks and Regenstein, 1970) The free energy change in the hydrolysis of MgATP to MgADP and Pi is ΔG' = –7.7 kcal mol−1 under the same conditions (Alberty, 1994). If these two reactions can be made to be interdependent, or coupled, the overall process would be the reaction of acetate, ethanol, and ATP to produce ethyl acetate, MgADP, and Pi, and the overall standard free energy change would be ΔG' = –3.7 kcal mol−1, making it a spontaneous or energetically downhill process. In the action of an ATP-dependent synthetase or ligase, the enzyme links the hydrolysis of MgATP with the ligation of the molecules by catalyzing the phosphorylation or adenylylation of one substrate and then the displacement of phosphate or AMP by the other substrate. Two types of glutamine synthetases are found in bacteria and eukaryotes. The bacterial glutamine synthetases, designated GS I (EC 6.3.1.2), are the most thoroughly studied. All species of GS I are dodecameric, 600- to 640-kDa enzymes assembled as two layers of hexameric rings associated face to face (Eisenberg et al., 2000; Stadtman and Ginsburg, 1974). Eukaryotic synthetases, designated GS II, are less understood, but essential aspects of their reaction mechanisms appear to be similar to that of GS I (Eisenberg et al., 2000; Meister, 1974a). Both GS I and GS II can be found in bacteria, although GS I is predominant. Eukaryotes contain only GS II. In this chapter, we discuss the reaction mechanism of GS I and GS II and the structure of GS I.

The structure of myosin and its role in energy transduction in muscle

1986 ◽  
Vol 64 (4) ◽  
pp. 265-276 ◽  
Author(s):  
John W. Shriver
Keyword(s):  
Muscle Contraction ◽  
Atp Hydrolysis ◽  
Structural Information ◽  
Force Production ◽  
Energy Transduction ◽  
Myosin Atpase ◽  
Structural Transitions ◽  
The Relationship ◽  
Hydrolysis Of ◽  
Present Understanding

The present understanding of the relationship between the structure of the myosin ATPase and its role in force production for muscle contraction is reviewed. Emphasis is placed on structural transitions in myosin that occur during ATP hydrolysis which may be correlated with force production. Although detailed structural information is presently lacking, numerous spectroscopic and kinetic experiments have indicated that myosin exists in two structural states for each chemical intermediate in the hydrolysis of ATP. Models are discussed which view a transition between these two states as the energy transduction "event" (i.e., force production).

scholarly journals Reformulation of an extant ATPase active site to mimic ancestral GTPase activity reveals a nucleotide base requirement for function

eLife ◽  
2021 ◽  
Vol 10 ◽  
Author(s):  
Taylor B Updegrove ◽  
Jailynn Harke ◽  
Vivek Anantharaman ◽  
Jin Yang ◽  
Nikhil Gopalan ◽  
...  
Keyword(s):  
Active Site ◽  
Atp Hydrolysis ◽  
Binding Pocket ◽  
Gtpase Activity ◽  
Biological Functions ◽  
Gtp Hydrolysis ◽  
Nucleotide Base ◽  
Nucleoside Triphosphates ◽  
Nucleotide Specificity ◽  
Hydrolysis Of

Hydrolysis of nucleoside triphosphates releases similar amounts of energy. However, ATP hydrolysis is typically used for energy-intensive reactions, whereas GTP hydrolysis typically functions as a switch. SpoIVA is a bacterial cytoskeletal protein that hydrolyzes ATP to polymerize irreversibly during Bacillus subtilis sporulation. SpoIVA evolved from a TRAFAC class of P-loop GTPases, but the evolutionary pressure that drove this change in nucleotide specificity is unclear. We therefore reengineered the nucleotide-binding pocket of SpoIVA to mimic its ancestral GTPase activity. SpoIVAGTPase functioned properly as a GTPase but failed to polymerize because it did not form an NDP-bound intermediate that we report is required for polymerization. Further, incubation of SpoIVAGTPase with limiting ATP did not promote efficient polymerization. This approach revealed that the nucleotide base, in addition to the energy released from hydrolysis, can be critical in specific biological functions. We also present data suggesting that increased levels of ATP relative to GTP at the end of sporulation was the evolutionary pressure that drove the change in nucleotide preference in SpoIVA.

Effect of Modifiers on the Hydrolysis of Basic and Neutral Peptides by Carboxypeptidase B

1975 ◽  
Vol 53 (7) ◽  
pp. 747-757 ◽  
Author(s):  
Graham J. Moore ◽  
N. Leo Benoiton
Keyword(s):  
Active Site ◽  
Active Sites ◽  
Kinetic Behavior ◽  
Carboxypeptidase A ◽  
Phenyllactic Acid ◽  
Carboxypeptidase B ◽  
Substrate Complex ◽  
Enzyme Substrate ◽  
Basic Peptides ◽  
Hydrolysis Of

The initial rates of hydrolysis of Bz-Gly-Lys and Bz-Gly-Phe by carboxypeptidase B (CPB) are increased in the presence of the modifiers β-phenylpropionic acid, cyclohexanol, Bz-Gly, and Bz-Gly-Gly. The hydrolysis of the tripeptide Bz-Gly-Gly-Phe is also activated by Bz-Gly and Bz-Gly-Gly, but none of these modifiers activate the hydrolysis of Bz-Gly-Gly-Lys, Z-Leu-Ala-Phe, or Bz-Gly-phenyllactic acid by CPB. All modifiers except cyclohexanol display inhibitory modes of binding when present in high concentration.Examination of Lineweaver–Burk plots in the presence of fixed concentrations of Bz-Gly has shown that activation of the hydrolysis of neutral and basic peptides by CPB, as reflected in the values of the extrapolated parameters, Km(app) and keat, occurs by different mechanisms. For Bz-Gly-Gly-Phe, activation occurs because the enzyme–modifier complex has a higher affinity than the free enzyme for the substrate, whereas activation of the hydrolysis of Bz-Gly-Lys derives from an increase in the rate of breakdown of the enzyme–substrate complex to give products.Cyclohexanol differs from Bz-Gly and Bz-Gly-Gly in that it displays no inhibitory mode of binding with any of the substrates examined, activates only the hydrolysis of dipeptides by CPB, and has a greater effect on the hydrolysis of the basic dipeptide than on the neutral dipeptide. Moreover, when Bz-Gly-Lys is the substrate, cyclohexanol activates its hydrolysis by CPB by increasing both the enzyme–substrate binding affinity and the rate of the catalytic step, an effect different from that observed when Bz-Gly is the modifier.The anomalous kinetic behavior of CPB is remarkably similar to that of carboxypeptidase A, and is a good indication that both enzymes have very similar structures in and around their respective active sites. A binding site for activator molecules down the cleft of the active site is proposed for CPB to explain the observed kinetic behavior.

A point-mass model of gibbon locomotion

1999 ◽  
Vol 202 (19) ◽  
pp. 2609-2617 ◽  
Author(s):  
J.E. Bertram ◽  
A. Ruina ◽  
C.E. Cannon ◽  
Y.H. Chang ◽  
M.J. Coleman
Keyword(s):  
Energy Exchange ◽  
Forest Canopy ◽  
Mechanical Energy ◽  
Single Point ◽  
Metabolic Cost ◽  
Point Mass ◽  
Mass Model ◽  
Natural Behavior ◽  
Continuous Contact ◽  
Mechanical Factors

In brachiation, an animal uses alternating bimanual support to move beneath an overhead support. Past brachiation models have been based on the oscillations of a simple pendulum over half of a full cycle of oscillation. These models have been unsatisfying because the natural behavior of gibbons and siamangs appears to be far less restricted than so predicted. Cursorial mammals use an inverted pendulum-like energy exchange in walking, but switch to a spring-based energy exchange in running as velocity increases. Brachiating apes do not possess the anatomical springs characteristic of the limbs of terrestrial runners and do not appear to be using a spring-based gait. How do these animals move so easily within the branches of the forest canopy? Are there fundamental mechanical factors responsible for the transition from a continuous-contact gait where at least one hand is on a hand hold at a time, to a ricochetal gait where the animal vaults between hand holds? We present a simple model of ricochetal locomotion based on a combination of parabolic free flight and simple circular pendulum motion of a single point mass on a massless arm. In this simple brachiation model, energy losses due to inelastic collisions of the animal with the support are avoided, either because the collisions occur at zero velocity (continuous-contact brachiation) or by a smooth matching of the circular and parabolic trajectories at the point of contact (ricochetal brachiation). This model predicts that brachiation is possible over a large range of speeds, handhold spacings and gait frequencies with (theoretically) no mechanical energy cost. We then add the further assumption that a brachiator minimizes either its total energy or, equivalently, its peak arm tension, or a peak tension-related measure of muscle contraction metabolic cost. However, near the optimum the model is still rather unrestrictive. We present some comparisons with gibbon brachiation showing that the simple dynamic model presented has predictive value. However, natural gibbon motion is even smoother than the smoothest motions predicted by this primitive model.

Sign in / Sign up

Export Citation Format

Share Document