B. Linearity of Initial Velocity with Enzyme Concentration

For the great majority of actual cases studied, the initial rate of enzyme reaction increases linearly with increasing enzyme concentration, as in Figure 4 (curve a) [20]. Indeed, this is necessary for modeling the effect of different levels of inhibition of an enzyme on an assay. However, this relationship must be experimentally verified, since departures from linearity are warning signs to look for artifacts in the assay system and many of them can be rectified experimentally. Some of the more common examples are

Displaced linear curve (Fig. 4, curve b): a toxic impurity poisons enzyme until free E overcomes the level of toxic impurity.

Figure 4 Examples of initial rate versus enzyme concentration plots with upwards curvature. Normal (a), toxic impurity (b), activator (c), active aggregated subunits (d), and complex subunit aggregation and activation (e).

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