Enzyme Kinetics -- Part I
Part III. Enzyme Catalyzed Rates at Different Substrate Concentrations.
Since the enzyme is used many times to catalyze the same reaction, the concentration of the enzyme is much less than the substrate:
[S] >> [E]
Thus, the substrate saturates the enzyme. This is best understood by observing the rate of the reaction or initial velocity at different [S] (ie. substrate concentrations):
Figure 3. Model data for the enzyme catalyzed reaction. These data show that at low [S], the initial velocity is more or less proportional to the [S]. At high [S], the initial velocity no longer increases as more substrate is added. Thus, at high [S] the enzyme is saturated with substrate and no increase in the enzyme catalyzed rate is observed.
This model set of data for an enzyme catalyzed reaction shows the initial velocity in terms of the amount of product formed per unit time (ie micromoles of product/min) at various substrate concentrations. These data can be plotted in a graphical form to also illustrate the results of an enzyme catalyzed reaction.
Figure 4. Plot of initial velocity of the enzyme catalyzed reaction (Vo) versus the [S] (ie substrate concentration). Initial velocity is always given in units of amount of product formed per unit time and the substrate concentration is given in molar units (ie mM).
Here it is easy to see the saturation of the enzyme at high [S] where the initial velocity approaches a limiting value. The plot has the shape of a square hyperbola.
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©Wilbur H. Campbell, 1995; wcampbel@mtu.edu