Isozyme

As isozyme (also isozyme ) refers to one of several forms of an enzyme, which all catalyze the same reaction, whereby the individual forms are different in the structure ( amino acid sequence ). Isoforms can be distinguished using the methods of enzyme kinetics and protein chemistry.

The relevance of the presence of several enzymes for one and the same reaction on the one hand in different kinetic parameters ( affinity, turnover number ) are, on the other hand can isoenzymes respond differently to regulatory signals (inhibitors, activators ).

The occurrence of isoenzymes highlights the following aspects:

• Finer control of metabolic reactions,
• Different metabolic patterns in various organs,
• Different localization and role of an enzyme in the metabolism within a cell type.

Examples

• Glucokinase ( liver, pancreas) / hexokinase ( ubiquitous )
• Lactate dehydrogenases from skeletal muscle (M- type ) or cardiac muscle (H- type); only the H44- enzyme is inhibited in the presence of NAD and pyruvate.
• Creatine kinases possess two subunits. KKmm are specifically present in skeletal muscle, KKbb in the brain and KKmb in the heart muscle.

• Enzyme