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E Pate

Publications and source records attributed to E Pate.

45 records · Page 3Linked to original sources
PubMed1986

A model for the interaction of muscle cross-bridges with ligands which compete with ATP.

A model is presented to describe the inhibition of muscle fiber contraction by ligands that compete with MgATP. Two ligands, adenosine 5' (beta, gamma-imido) triphosphate (AMPPNP) and pyrophosphate (PPi), decrease the force developed in isometric contractions and act as weak competitive inhibitors of the maximum velocity of contraction (Pate & Cooke, 1985). These observations provide information on the energetics of actomyosin ligand states at the end of the power-stroke where MgATP dissociates the myosin cross-bridge from actin, and they are analysed in terms of a seven state model of cross-bridge kinetics. The model can reconcile the observations that these ligands bind tightly to fibers, Kd = 10(-4) M, while they are only weak inhibitors of fiber velocity, Ki = 2 X 10(-3) M. It provides a reasonable fit to the data and leads to several conclusions concerning the properties of the cross-bridge states. The states with bound ligand are shifted axially so that they occur earlier in the power-stroke than the nucleotide-free rigor state. This shift also explains the axial lengthening seen upon addition of ligands to rigor fibers. We can conclude that these ligands cause small perturbations in the cross-bridge configuration rather than large shifts. A second conclusion is that cross-bridges do not detach from actin during their power-strokes. Instead they traverse the entire length of the power stroke and are detached only at the end, leading to the suggestion that the cycling of bridges in isometric fibers is due to fluctuations in the relative positions of thick and thin filaments. With some further assumptions, the model also explains many of the rate constants and equilibrium constants of the actin-myosin-ligand interaction that have been measured in solution.

Adenosine Triphosphate↗
PubMed1985

The effects of ADP and phosphate on the contraction of muscle fibers.

The products of MgATP hydrolysis bind to the nucleotide site of myosin and thus may be expected to inhibit the contraction of muscle fibers. We measured the effects of phosphate and MgADP on the isometric tensions and isotonic contraction velocities of glycerinated rabbit psoas muscle at 10 degrees C. Addition of phosphate decreased isometric force but did not affect the maximum velocity of shortening. To characterize the effects of ADP on fiber contractions, force-velocity curves were measured for fibers bathed in media containing various concentrations of MgATP (1.5-4 mM) and various concentrations of MgADP (1-4 mM). As the [MgADP]/[MgATP] ratio in the fiber increases, the maximum velocity achieved by the fiber decreases while the isometric tension increases. The inhibition of fiber velocities and the potentiation of fiber tension by MgADP is not altered by the presence of 12 mM phosphate. The concentration of both MgADP and MgATP within the fiber was calculated from the diffusion coefficient for nucleotides within the fiber, and the rate of MgADP production within the fiber. Using the calculated values for the nucleotide concentration inside the fiber, observed values of the maximum contraction velocity could be described, within experimental accuracy, by a model in which MgADP competed with MgATP and inhibited fiber velocity with an effective Ki of 0.2-0.3 mM. The average MgADP level generated by the fiber ATPase activity within the fiber was approximately 0.9 mM. In fatigued fibers MgADP and phosphate levels are known to be elevated, and tension and the maximum velocity of contraction are depressed. The results obtained here suggest that levels of MgADP in fatigued fibers play no role in these decreases in function, but the elevation of both phosphate and H+ is sufficient to account for much of the decrease in tension.

Adenosine Diphosphate↗
PubMed1985

The inhibition of muscle contraction by adenosine 5' (beta, gamma-imido) triphosphate and by pyrophosphate.

We have studied the inhibition of the contraction of glycerinated rabbit psoas muscle caused by ligands that bind to the ATPase site of myosin. Two ligands, adenosine 5' (beta, gamma-imido) triphosphate (AMPPNP) and pyrophosphate (PPi), decreased the force and stiffness developed in isometric contractions and the velocity of shortening of isotonic contractions. The force exerted by isometric fibers was measured as a function of MgATP in the presence and absence of a constant concentration of the ligands. As the MgATP concentration decreased, the inhibition of tension caused by the ligand increased, reaching approximately 50% at 25 microM MgATP and either 2 mM MgPPi or 2 mM MgAMPPNP. The maximum velocity of shortening was also measured as a function of MgATP concentration in the presence of 1 and 2 mM MgPPi and 2.5 and 5 mM MgAMPPNP. Both ligands acted as pure competitive inhibitors with Ki = 3.0 mM for PPi and 5.1 mM for MgAMPPNP. These data show that both ligands are weak inhibitors of the contraction of fibers. The results provided information on the energetics of actin-myosin-ligand states that occur in the portion of the cross-bridge cycle where MgATP binds to myosin. A simple analysis of the inhibition of velocity suggests that MgAMPPNP binds to the actomyosin complex at this step of the cycle with an effective affinity constant of approximately 2 X 10(2) M-1.

Adenosine Triphosphate↗
PubMed1984

The organizer region and pattern regulation in amphibian embryos.

The cellular proportions in the dorsal-to-ventral, mesodermal sequence of pattern elements in the gastrula of certain amphibian embryos regulate with respect to embryo size. The dorsal, blastoporal lip serves as an organizer for this developmental sequence and the grafting of an additional organizer into a ventral location results in a symmetric pattern of cell types. A size-regulating, reaction-diffusion model is presented which produces positional information for development consistent with experimental observations in normal amphibian development and in the presence of an additional, ventrally-located, organizer region.

Amphibians↗
PubMed1984

Applications of a model for scale-invariant pattern formation in developing systems.

A fundamental problem in developmental biology concerns the proportioning of the developing tissue of a morphallactic system into different cell types in a way that is independent of the overall size of the tissue. The two main models for positional information in pattern formation, the source-sink models and the Turing reaction-diffusion models, have shortcomings that limit their applicability. In a previous paper, we described a model that can produce perfectly scale-invariant spatial patterns and analyzed some of its mathematical properties. In the present paper, we demonstrate some of the shortcomings of the standard reaction-diffusion models and discuss the applicability of our model to developmental systems.

Animals↗
PubMed1980

Scale-invariance in reaction-diffusion models of spatial pattern formation.

We propose a reaction-diffusion model of spatial pattern formation whose solutions can exhibit scale-invariance over any desired range for suitable choices of parameters in the model. The model does not invoke preset polarity or any other ad hoc distinction between cells and provides a solution to the French flag problem without sources at the boundary. Furthermore, patterns other than the polar pattern that usually arises first in a growing one-dimensional system described by Turing's model can be obtained. Evidence is given that suggests that the model may apply in the slug stage of Dictyostelium discoideum.

Cell Differentiation↗
PubMedDate not supplied

Synthesis and characterization of novel spin-labeled photoaffinity nonnucleoside analogues of ATP as structural and EPR probes for myosin.

Two new spin-labeled photoreactive nonnucleoside ATP analogues, 1-(4-azido-2-nitrophenyl)amino-3-(1-oxyl-2,2,5, 5-tetramethylpyrrolidinyl-3-carbamido)-2-propyl triphosphate (SL-NANTP) and 2-(4-azido-2-nitrophenyl)amino-2,2-(1-oxyl-2,2,6, 6-tetramethyl-4-piperidylidene)di(oxymethylene) ethyl triphosphate (SSL-NANTP), were synthesized and characterized. This study aims to develop a second generation of NANTP-based analogues containing immobile spin labels that can be used to monitor conformational changes in myosin during the contractile cycle of muscle. Previous studies have shown that both a photoaffinity nonnucleoside ATP analogue, 2-[(4-azido-2-nitrophenyl)amino] ethyl triphosphate (NANTP) [Nakamaye et al. (1985) Biochemistry 24, 5226-5235], and a photoaffinity ATP analogue, 3'(2')-O-4-[4-oxo-(4-amino-2,2,6, 6-tetramethyl-piperidino-1-oxyl)-4-benzoyl] benzoyl adenosine 5'-triphosphate (SL-Bz(2)ATP) [Wang et al. (1999) J. Muscle Res. Cell Motil. 20, 743-753], behave like ATP in their interactions with myosin. Remarkably, photolabeled myosin recovers all of its normal enzymatic properties after treatment with actin in the presence of MgATP [Luo et al. (1995) Biochemistry 34, 1978-1987]. For SL-NANTP, the spin label moiety is attached to NANTP via an aminomethyl side chain. In SSL-NANTP, attachment is via a restricted spiro ring. The two new probes interact with myosin subfragment-1 (S1) in a manner analogous to ATP, and after photoincorporation, labeled S1 recovers full activity after treatment with actin and MgATP. The electron paramagnetic resonance (EPR) spectrum resulting from S1 photolabeled with SL-NANTP shows a very high degree of probe mobility. However, the EPR spectrum of S1 photolabeled with SSL-NANTP shows that the probe is highly immobilized with respect to S1, constrained to move within a cone of angle 52 degrees (full-width, half-max). Unlike the parent, NANTP, which photolabels on the 23 kDa tryptic fragment of S1, SSL-NANTP photolabels on the 20 kDa fragment. Its highly immobile nature means that it is potentially a useful reporter group to monitor cross-bridge motion in muscle fibers.

Actins↗