Contribution to the standardization of influenza neuraminidase inhibition tests, based on enzyme- antienzyme kinetic studies.

1. From enzyme-antienzyme kinetic studies a method for the determination of anti-n2-neuraminidase antibodies has been developed. This procedure is applicable in routine diagnosis. 2. Considering the present conditions, the reversibility of the virus neuraminidase antigen-antineuraminidase antibody complex has been proved. The inhibition must be described as a non-competitive one. 3. As a reference value for comparative immunity estimations the relative antibody concentration T150 is defined as the point of reciprocal serum dilution, where under a given substrate concentration the inhibited enzyme activity vi is half of the non-inhibited enzyme activity vo. 4. For the calculation of T150 a simple formula is derived from the Michaelis-Menten kinetic. Under present conditions the value of T150 is in a range of 1.5 log 2 dilution steps plus or minus the specific serum dilution T150 uninfluenced by possible variable parameters such as enzyme activity, substrate concentration and inhibitor concentration.