Katz mechanism

The del Castillo-Katz Mechanism 1. Relationship between Agonist Concentration and Fraction of Receptors in an Active Form... 

The term state rather than condition is often used in this context. However, the latter seems preferable in an introductory account. This is because the del Castillo-Katz mechanism is often described as a two-state model of receptor action, meaning here that the occupied receptor exists in two distinct (albeit interconvertible) forms, AR and AR, whereas three conditions of the receptor (R, AR, and AR ) have to be identified when applying the law of mass action to the binding of the ligand, A. 

The del Castillo-Katz Mechanism 2. Interpretation of Efficacy for Ligand-Gated Ion Channels... 

A first step is to recast Stephensons s equations in terms of total receptor occupancy (pocc, occupied but inactive plus occupied and active). Taking this course, and assuming that the del Castillo-Katz mechanism applies in its simplest form (Eq. (1.7)), we can write ... 

This relationship has often been used to obtain evidence that two antagonists act at the same site. It can also be derived by taking the Gaddum equation as the starting point rather than expressions based on the del Castillo-Katz mechanism. 

The membrane potential in biology came to prominence in the days in which electrode phenomena were treated exclusively in terms of equilibrium thermodynamics. Between 1892 (Nernst ) and 1911 (Donnan " ), three treatments were given of membrane potentials. They form such a durable part of electrochemistry, not because of their importance per se, or even of their direct relevance to biological phenomena, but because one of them was the origin of the best-known of bioelectrochemical theories, the Hodgkin-Huxley-Katz mechanism for the passage of electricity through nerves. 

Katz has proposed a carbenic Chauvin-type metathesis mechanism for the polymerization of alkynes. This mechanism involves two alkynes coordinated to in the catalytically active species. The ETC catalyzed ligand exchange process is adequate to rapidly introduce two or three alkyne ligands on in such a way that the Katz mechanism is then operating as shown on the following scheme. 

Alkyne polymerization can be initiated by metal-alkylidenes or metal-alkylidyne complexes. The mechanism involves metallacyclobutene or metallacyclobutadiene key intermediates, in the same way as alkene metathesis and ROM involve metal-lacyclobutane intermediates Katz mechanism, bottom of this page, an extension of the hauvin mechanism for alkyne metathesis. For instance, Schrock s catalyst W - u O - u 3, shown in section. as catalyst of disynunetrical alkyne metathesis, also initiates the polymerization of acetylene and terminal alkynes rather than metathesizing them. Indeed, the molecules of terminal alkynes successively insert into the W- bond of the metallacyclobutadiene intermediate... 

The drag coefficients for disks (flat side perpendicular to the direction of motion) and for cylinders (infinite length with axis perpendicular to the direclion of motion) are given in Fig. 6-57 as a Function of Reynolds number. The effect of length-to-diameter ratio for cylinders in the Newton s law region is reported by Knudsen and Katz Fluid Mechanics and Heat Transfer, McGraw-Hill, New York, 1958). 

Generation Spontaneous generation of gas bubbles within a homogeneous liquid is theoreticaUy impossible (Bikerman, Foams Theoiy and Industrial Applications, Reinhold, New York, 1953, p. 10). The appearance of a bubble requires a gas nucleus as avoid in the liquid. The nucleus may be in the form of a small bubble or of a solid carrying adsorbed gas, examples of the latter being dust particles, boiling chips, and a solid wall. A void can result from cavitation, mechan-ic ly or acoustically induced. Blander and Katz [AlChE J., 21, 833 (1975)] have thoroughly reviewed bubble nucleation in liquids. 

Hulburt, H.M. and Katz, S., 1964. Some problems in particle technology - a statistical mechanical fomiulation. Chemical Engineering Science, 19, 555-574. 

Thermodynamic and mechanical equilibrium on a curved vapor-liquid interface requires a certain degree of superheat in order to maintain a given curvature. Characteristics of homogeneous and heterogeneous nucleation can be estimated in the frame of classical theory of kinetics of nucleation (Volmer and Weber 1926 Earkas 1927 Becker and Doring 1935 Zel dovich 1943). The vapor temperature in the bubble Ts.b can be computed from equations (Bankoff and Flaute 1957 Cole 1974 Blander and Katz 1975 Li and Cheng 2004) for homogeneous nucleation in superheated liquids... 

The first physically plausible mechanism for receptor activation was proposed by del Castillo and Katz (1957). They made the important distinction that agonist binding and channel opening of the AChR must occur as two separate steps ... 

Katz, R.J. Role of serotonergic mechanisms in animal models of predation. Prog Neuropsychopharmacol 4 219-231, 1980. 

The simplest agonist mechanism that can be used to describe activation of the ligand-gated ion-channel receptors is that first suggested by del Castillo and Katz (1957) for activation of nAChRs at the neuromuscular junction ... 

Burch (1983) suggests that repair mechanisms cause a non neglectible complication for extrapolation from high to low doses and presents a modification of the linear-quadratic formula given above. Katz and Hofmann (1982) carried out an analysis of particle tracks with the result that they find no basis for a linear or linear-quadratic extrapolation to low doses. Van Bekkum and Bentvelzen (1982) present a hypothesis of the gene transfer-... 

Cram and co-workers have been successful in modifying certain of their cavitands such that reactions with a bound substrate are promoted. Such systems provide a first step towards the synthesis of rudimentary enzymes (Cram, Katz, Dicker, 1984). One example of this type, involving a binding step followed by a fast acylation step, is illustrated by Figure 5.1. This sequence resembles part of the mechanism used by chymo-trypsin to cleave a peptide bond. Thus, the enzymic process entails several stages but, like the model system, begins with a binding step followed by a crucial transacylation step. 

Quantal analysis defines the mechanism of release as exocytosis. Stimulation of the motor neuron causes a large depolarization of the motor end plate. In 1952, Fatt and Katz [11] observed that spontaneous potentials of approximately 1 mV occur at the motor endplate. Each individual potential change has a time course similar to the much larger evoked response of the muscle membrane that results from electrical stimulation of the motor nerve. These small spontaneous potentials were therefore called... 

Tijssen, R., The mechanism and importance of zone-spreading, In Katz, E., Eksteen, R., Schoenmakers, P. and Miller, N., Eds., Handbook of HPLC, Marcel Dekker, New York, 1998. 

Studies with VSV and SFV were the first to show that membrane glycoproteins make use of the same mechanisms used by secretory proteins to become segregated into the ER lumen (Katz et al., 1977 Rothman and Lodish, 1977 Wirth et al., 1977 Lingappa et al., 1978 ... 

Lyons. C.D., Katz. S.. and Bartha, R. Mechanisms and pathways of aniline elimination from aquatic environments. Appl. Environ. Microbiol., 48(3) 491-496,1984. 

Gallagher, KJ. Feifknecht,W. Marmweiler, U. (1968) Mechanism of oxidation of magnetite to Y-Fe20j. Nature 217 1118-1121 Gallias, J.L. (1998) Microstructure of the interfacial transition zone around corroded reinforcements. In Katz, A. Benier, M. Alexander, M. Arliguie, G. (eds.) The interfadal transition zone in cementitions composites. E.F.N. Spon, London, 171-178 Galvez, N. Barron,V. Torrent, J. (1999) Preparation and properties of hematite with structural phosphorus. Clays Clay Miner. 47 375-385... 

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