Other Factors Affecting Initial Velocity

Enzymatic reactions are influenced by a variety of solution conditions that must be well controlled in HTS assays. Buffer components, pH, ionic strength, solvent polarity, viscosity, and temperature can all influence the initial velocity and the interactions of enzymes with substrate and inhibitor molecules. Space does not permit a comprehensive discussion of these factors, but a more detailed presentation can be found in the text by Copeland (2000). Here we simply make the recommendation that all of these solution conditions be optimized in the course of assay development. It is worth noting that there can be differences in optimal conditions for enzyme stability and enzyme activity. For example, the initial velocity may be greatest at 37°C and pH 5.0, but one may find that the enzyme denatures during the course of the assay time under these conditions. In situations like this one must experimentally determine the best compromise between reaction rate and protein stability. Again, a more detailed discussion of this issue, and methods for diagnosing enzyme denaturation during reaction can be found in Copeland (2000). 

It is almost always the case that enzymes are most active under the solution conditions that best match the physiological conditions experienced by the enzyme. There are, however, exceptions to this generalization. Sometimes one will find that the laboratory conditions that maximize catalytic activity are different from one s expectation of physiological conditions. In such cases a careful judgment must be made about what conditions to use for screening purposes. Whenever possible, my bias is to screen at conditions that most closely match the physiological conditions, 

In some cases one s best guess at physiological conditions does not support sufficient catalytic activity to make a screening assay feasible. In this situation one has no choice but to compromise in favor of more optimal laboratory conditions. Nevertheless, one should attempt, whenever possible, to come as close as feasible to assay conditions that reflect the physiological context in which the target enzyme operates. 

The discussion above was concerned with the effects of solution conditions on enzyme activity, hence reaction velocity. Equally important for the purpose of assay design is the influence of specific solution conditions on the detection method being used. This latter topic is beyond the scope of the present text. Nevertheless, this is an important issue for screening scientists whose job is often to balance the needs of biochemical rigor and assay practicality in development of an HTS assay. An 

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In addition to the above there are other factors that affect the corrosion rate. Included are initial exposure conditions, sample mass, orientation, extent of sheltering, wind velocity, nature of the corrosion products formed, and pollutants present (both known and unknown). 

In searching for new explosives one is most concerned with performance (detonation velocity and pressure), thermal properties, and sensitivity. Whether a new candidate explosive is ultimately widely used may well be determined by other factors, such as cost, toxicity, melting point, etc., but the initial research effort is guided by the trinity of performance, thermal stability, and sensitivity. This presents a difficult multifactoral problem in assessing the various molecular properties that contribute to each of these principal selection criteria. For instance, detonation velocity is affected by density, elemental composition, and heat of formation. These factors must be varied together in such a way as to maximize the combined effect on performance. 

Alumina and other ceramic membranes of various microfiluaiion pore sizes have been used for the separation of yeast (saccharomyces cerevisiae) from the broth and the clarification of thin stillage [Cheryan, 1994]. A typical flux of 110 L/hr-m can be obtained with a crossflow velocity of 4 m/s and a transmembrane pressure of 1.7 bars. The crossflow velocity is found to markedly affect the membrane flux. Concenuation factors (ratios of final to initial concentrations) of 6 to 10 for both the broth and the stillage can be achieved. Backflushing with a frequency of every 5 minutes and a duration of 5 seconds helps maintain the flux, particularly in the initial operating period. The permeate flux for both types of separation reaches steady state after 30 to 90 minutes. 

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