Substrate and enzyme concentration

The normal  pattern  of dependence  of enzyme  rate on substrate  concentration ([S])  is  which  at  low  substrate  concentrations   a  doubling  of  [S]  will  lead  to  a doubling of the initial velocity (V₀). Though, at higher substrate concentrations the enzyme becomes further and saturated increases in [S] lead to very small changes in V₀. This happens because at saturating substrate concentrations effectively all of the enzyme molecules have bound substrate.  The whole  enzyme rate is now dependent  on the rate at that the product can dissociate  from the enzyme and  adding  additional  substrate  will  not  affect  this.  The shape of the consequential graph when V0 is plotted against [S] is known a hyperbolic curve.

In conditions where the substrate concentration is saturating for instance the entire enzyme molecules are bound to substrate a repetition of the enzyme concentration will lead to a doubling of V₀.  This will gives a straight line graph when V₀ is plotted against enzyme concentration.

           Figure: The relationship between substrate concentration [S] and initial reaction velocity (V0).

even little changes in the 3-D shape of the enzyme can alter the structure of the active site and lead to a reduce in catalytic activity. The whole effect of an increase in temperature on the reaction rate of the enzyme is a balance among these two opposing effects. The graph of temperature plotted against V0 will thus show a curve with a well-de?ned temperature optimum. For several mammalian enzymes this is around 37^.C but there are also organisms that have enzymes adapted to working at considerably lower or higher temperatures.   For  instance,  Taq  polymerase  which  is  used  in  the  polymerase chain reaction, is found in a bacterium which lives at high temperatures  in hot springs  and therefore  is adapted  to work  optimally  at high  temperatures.