Hit kinetics

Emmelot P, Scherer E. Multi-hit kinetics of tumor formation, with special reference to experimental liver and human lung carcinogenesis and some general conclusions. Cancer Res. 1977 37(6) 1702-1708. 

RNA interaction and therefore cannot be recommended for probing experiments (e.g. RNase SI and RNase U2 have a pH optimum of 4.5 which prevents or destabilises protein-RNA complex formation). RNase A has a high affinity for a pyrimidine-adenosine stretch (particularly UA), so it can therefore be difficult to obtain single-hit kinetics (except for the UA sequence). Furthermore, RNase A exhibits an endogenous helix unfolding property which makes structure assignment difficult. RNases such as RNase CL3 and a-sarcin are inhibited by Mg2+ which is required for the stability of many complexes and also for proper folding of RNA. 

Fig. 4.13. Flow chart of the protein footprinting technique. Purified recombinant protein, which has been radioactively labelled at the N- or C-terminal, is cleaved by proteinases or chemicals with single-hit kinetics. The substrate is kept at native conditions in uncomplexed and complexed form. The cleavage products are analysed in high resolution SDS gels.

Ideally, dose-response curves follow simple relations they are either linear (Fig. 2) or else follow a two-hit kinetics function. Such situations can be found at lower dose ranges, but at higher doses curves can plateau or even decline. Extensive investigation of dose-response relationships with chemically induced mutation has been reported by Heslot i ) nd Schwaier and by Kplmark in Neurospora. 

It is not known whether one or both of the two types of AAV virions is individually capable of initiating a productive infection in the presence of adenovirus or whether both types of AAV particles are required. Titration studies of AAV infectivity in the presence of excess adenovirus have suggested single-hit kinetics for infection this would imply that it is not essential for both types of co-infect a cell (Blacklow et al., 1967). Attempts to productively infect cells with physically separated particles (Berns and Adler, 1972) have been made but the data have not been of sufficient precision to resolve this problem (Hoggan and Berns, unpublished data). Purified AAV DNA has been shown to be infectious in the presence of helper adenovirus (Hoggan et al., 1968). The infectivity of the DNA was increased by the addition of... 

To substantiate this concept, the present set of experiments should be complemented by analogous data from transfection experiments with phage DNAs showing single-hit kinetics due to transfection with monomeric molecules. The model would predict that in these cases transfection crosses would not yield results which are basically different from normal phage crosses. Unfortunately, 029 can not be used for this purpose. 029 DNA molecules show a tendency to aggregate (Hirokawa, unpublished). Studies of genetic recombination in the SPO 2 system are presently under way in our laboratory. 

Under constant experimental conditions, the number of plaques induced is proportional to the dilution factor, indicating that one RNA molecule is able to induce a replication cycle. The correlation between the number of plaques induced and the concentration of RNA during seeding in hypertonic solution indicates that the RNA does not aggregate under these experimental conditions. Furthermore, the inactivation of RNA infectivity by different methods follows first-order or one-hit kinetics only those RNA molecules which contain the RNA equivalent of one virus particle are infectious. 

It must also be realized that this thin surface region is in a very turbulent state. Since the liquid is in equilibrium with its vapor, then, clearly, there is a two-way and balanced traffic of molecules hitting and condensing on the surface from the vapor phase and of molecules evaporating from the surface into the vapor phase. From the gas kinetic theory, the number of moles striking 1 cm of surface per second is... 

It is instructive to consider just how mobile the surface atoms of a solid might be expected to be. Following the approach in Section III-2, one may first consider the evaporation-condensation equilibrium. The number of molecules hitting a 1-cm surface per second is from kinetic theory... 

INS Ion neutralization An inert gas hitting surface is spectroscopy [147] neutralized with the ejection of an Auger electron from a surface atom Spectroscopy of Emitted Ions or Molecules Kinetics of surface reactions chemisorption... 

MBRS Molecular beam spectroscopy [158] A modulated molecular beam hits the surface and the time lag for reaction products is measured Kinetics of surface reactions chemisorption... 

The acconunodation coefficient for Kr on a carbon filament is determined experimentally as follows. The electrically heated filament at temperature 72 is stretched down the center of a cylindrical cell containing Kr gas at 7. Gas molecules hitting the filament cool it, and to maintain its temperature a resistance heating of Q cal sec cm is needed. Derive from simple gas kinetic theory the expression... 

Mention was made in Section XVIII-2E of programmed desorption this technique gives specific information about both the adsorption and the desorption of specific molecular states, at least when applied to single-crystal surfaces. The kinetic theory involved is essentially that used in Section XVI-3A. It will be recalled that the adsorption rate was there taken to be simply the rate at which molecules from the gas phase would strike a site area times the fraction of unoccupied sites. If the adsorption is activated, the fraction of molecules hitting and sticking that can proceed to a chemisorbed state is given by exp(-E /RT). The adsorption rate constant of Eq. XVII-13 becomes... 

But k must always be greater than or equal to k h / (A i + kf). That is, the reaction can go no faster than the rate at which E and S come together. Thus, k sets the upper limit for A ,. In other words, the catalytic effieiency of an enzyme cannot exceed the diffusion-eontroUed rate of combination of E and S to form ES. In HgO, the rate constant for such diffusion is approximately (P/M - sec. Those enzymes that are most efficient in their catalysis have A , ratios approaching this value. Their catalytic velocity is limited only by the rate at which they encounter S enzymes this efficient have achieved so-called catalytic perfection. All E and S encounters lead to reaction because such catalytically perfect enzymes can channel S to the active site, regardless of where S hits E. Table 14.5 lists the kinetic parameters of several enzymes in this category. Note that and A , both show a substantial range of variation in this table, even though their ratio falls around 10 /M sec. 

C06-0036. Explain how each of the following observations is consistent with conservation of energy (a) An apple gains kinetic energy as it falls from a tree, (b) When that apple hits the ground. It loses Its kinetic energy. 

HTS data and secondary screening for hit validation and determination of kinetic on/off rates. These data have been successfully incorporated into hit triage by enhancing the understanding of SAR differences between potential scaffolds [24]. In this example, those differences allowed informed decision making in the choice of which series to pursue and which to deprioritize. 

At the hit triage stage, it is most common to be able to characterize sets of compounds in a kinetic solubility assay. In the assessment and utilization of these data, the potential disconnects between kinetic and thermodynamic solubility must be considered. Low kinetic solubility for a series of compounds should lead a project team to be concerned about the behavior of compounds in biological assays and buffers, as well as the potential for optimizing drug-like properties in that series. Conversely, while high kinetic solubility is a desirable property, chemists should still remain cognizant of the need to assess thermodynamic solubility as compounds are further optimized. 

During the characterization process, hits are typically tested for kinetic solubility and permeability in a model of passive diffusion such as PAMPA [22]. As new compounds are synthesized, additional parameters also need to be considered, such as pZa, chemical and plasma stability, and protein binding. Calculated properties such as MW, clogP, and PSA should also be tracked. 

Kinetic molecular theory explains why gases exert pressure. The constant bombardment of the walls of the vessel by the gas molecules, like the hitting of a target by machine gun bullets, causes a constant force to be applied to the wall. The force applied, divided by the area of the wall, is the pressure of the gas. 

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