Isozymes and Allosteric Enzymes

Many enzymes exist in more than one molecular form. These isozymes catalyze the same reaction but exhibit different kinetic properties (Km and tfmax values) and amino acid sequences. This means that their structural differences are genetically determined. Thus, all isozymes of 

Allosteric enzymes are oligomeric proteins exhibiting a sigmoidal dependence of the reaction rate on substrate concentration instead of a normal , hyperbolic (classical Michaelis-Menten) one. At first the rate increases only slightly with increasing substrate concentration there is then a rapid increase until near the maximum rate. This behaviour results from the presence of a regulatory allosteric center located on the same or another subunit as the catalytic center. This center may interact 

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