Saxitoxin (STX) is a toxin which is found in marine microorganisms. It is most likely synthesized by bacteria which live in symbiosis with dinoflagellates, a component of phytoplankton. Through the marine food chain, it can lead to poisoning of humans. The mechanism of toxicity of saxitoxin is vety similar to that of tetrodotoxin. Saxitoxin binds from the outside of the membrane to various forms of voltage-sensitive Na+channels and blocks the channel in an activation state-independent manner. [Pg.1110]

In the three-dimensional stmcture of actin, the environment of the phosphate moiety of the nucleotide appears roughly the same when CaADP or CaATP is bound. This observation argues against two different conformations. The reason why this is so is unclear. However, it must be stressed that the three-dimensional stmcture is derived from X-ray diffraction of crystals of the DNasel-actin complex, which, like G-actin, is unable to hydrolyze ATP. The conformation obtained may therefore correspond to G-actin frozen in the G-ATP state independently of the bound nucleotide. Stmctural studies in conjunction with site-directed mutagenesis experiments should eventually solve this problem. [Pg.49]

The prevalent receptor model for the excitatory amino acid is a tetrameric complex. As mentioned in the text, there is evidence that the channel conductance depends on the number of subunits that bind a ligand. Estimate the EC50 value and Hill coefficient for a dose-response curve assuming that the occupation at each subunit has a Kd value of 1 pi I, an % of 1, and that activation induces a transition to an active state independent of the state of the other subunits ... [Pg.128]

It is noted that all systems in turmoil tend to subside spontaneously to simple states, independent of previous history. It happens when the effects of previously applied external influences damp out and the systems evolve toward states in which their properties are determined by intrinsic factors only. They are called equilibrium states. Experience shows that all equilibrium states are macroscopically completely defined by the internal energy U, the volume V, and the mole numbers Nj of all chemical components. [Pg.409]

Description of a thermodynamic system requires specification of the way in which it interacts with the environment. An ideal system that exchanges no heat with its environment is said to be protected by an adiabatic wall. To change the state of such a system an amount of work equivalent to the difference in internal energy of the two states has to be performed on that system. This requirement means that work done in taking an adiabatically enclosed system between two given states is determined entirely by the states, independent of all external conditions. A wall that allows heat flow is called diathermal. [Pg.409]

Dr. Zuckerman We would also need an equal or more powerful test to tell us the valence state independent of Mossbauer experiments in... [Pg.164]

The general observation in the published work has been that for species such as hexamminechromium, thiocyanatopentammine, or the hexa-aquo ion where O18 exchange was looked at, irradiation produced a substitution reaction and nothing else. Moreover the reaction mode was independent of wave length, and the quantum yields did not change much. From a morphological point of view, there are essentially three types of explanations. First all excited states independently lead to the same chemical sequence, and we suppose that the primary act is simply a heterolytic bond fission. [Pg.250]

Palenik, G. J. (1997a). Bond valence sums in coordination chemistry using oxidation state independent Rq values. Inorg. Chem. 36, 122. [Pg.264]

For non-S -states the state-independent logarithm squared term disappears and the single-logarithmic contribution has the form... [Pg.49]

As was mentioned above, short distance contributions are state independent and always cancel in the differences of the form Z = n AE nS) — AE 1S). This means that such state-dependent differences of energies contain only contributions of large distances and are much easier to calculate. [Pg.57]

In this notation we have separated the state-independent contribution 562(15) originating exclusively from the short distances, first time obtained in [101], from the other contributions to this coefficient. The short distance contributions cancel in the difference 562(15) — Be2 nS) which corresponds to the energy shifts combination Z = n AE nS) — AE IS). This difference 562(15) — 562 ( u5) was independently calculated earlier in the framework of the effective potential approach [104, 105, 106, 107], and we will briefly describe this calculation. [Pg.62]

The state-independent high-frequency contribution as well as the low-frequency logarithmic term are different from zero only for the S -states and may easily be calculated with the help of (4.5)... [Pg.86]

A tedious third order perturbation theory calculation [16, 17] produces some additional state-independent terms with the net result being a few percent different from the naive result above. The additional state-independent contribution beyond the naive result above has the form [20]... [Pg.123]

As usual this logarithmic contribution is state-independent. Calculation of the nonlogarithmic contribution turned out to be a much more complicated task and the whole machinery of the relativistic two-particle equations was used in this work. First, the difference AE 1S) — 8AE 2S) was calculated [10], then some nonlogarithmic contributions of this order for the lA level were obtained [11], and only later the total nonlogarithmic contribution [12, 13] was obtained... [Pg.196]

State-independent contributions to the Lamb shift scale as 1/n and vanish in the difference Z = n Pi(nP) — EL nS), which may be calculated more... [Pg.235]

Both dissociation and disenablement can already be achieved in animals. With respect to dissociation, the PGO waves that are evoked by cholinergic microstimulation with carbachol can be state independent in two experimental paradigms short-term and long-term REM enhancement. By short term I mean four to six hours and by long term I mean six to ten days of altered function. The differences between the two syndromes appear to derive only from the very small distance between the two lateral brain stem sites from which they are evoked. [Pg.148]

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