Enzyme Immunoassays El and ELISA

Enzymes are one of the most commonly used labels in immunoassay. They enable measurement with a sensitivity close to that reached by radio-immunoassays but without the health hazards associated with radioactive substances. Enzyme immunoassays (El) and most importantly enzyme-linked immunosorbent 

The enzyme-catalysed reaction from substrate to product usually proceeds in two steps (equation 5.2). First, the substrate (S) reversibly binds to a specific site on 

1 oxido-reductase (dehydrogenase, oxidase, peroxidase, oxygenase) oxidation-reduction 

The turnover of the enzyme, A 3, is a measure of how many molecules of substrate can be converted to the product within a period of time. The rate of the reaction, V, can be described by the Michaelis-Menten equation  

The reaction rate depends on the concentrations of the enzyme [ ] and the substrate [5], as well as on the turnover number, ks, and the Michaelis-Menten-constant (Km), which, broadly speaking, quantifies the enzyme s affinity for its substrate. The catalytic activity of an enzyme also depends on temperature, pH, ionic strength and the presence of inhibitors or activators. For a more detailed discussion of enzyme kinetics, refer to one of the biochemistry textbooks listed at the end of this chapter. A suitable enzyme for labelling must be stable under the necessary reaction conditions and it must have a high turnover rate. 

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