Abstract: An optical method has been developed to find $alpha@1- antitrypsin unknown concentrations in human serum samples. This method applies light scattering properties exhibited by initially formed enzyme-inhibitor complexes and uses the curves of aggregation kinetics. It is independent of molecular hydrodynamics. Theoretical approaches showed that scattering properties of transient complexes obey the Rayleigh-Debie conditions. Experiments were performed on the Trypsin/$alpha@1-antitrypsin system. Measurements were performed in newborn, adult and pregnant sera containing $alpha@1-antitrypsin in the Trypsin excess region. The solution was excite by a He-Ne laser beam. SO, the particles formed during the reaction are scattering centers for the interacting light. The intensity of the scattered light at 90 degrees from incident beam depends on the nature of those scattering centers. Th rate of increase in scattered intensity depends on the variation in size and shape of the scatterers, being independent of its original size. Peak values of the first derivative linearly correlate with the concentration of $alpha@1-antitrypsin originally present in the sample. Results are displayed 5 minutes after the initiation of the experimental process. Such speed is of great importance in the immuno-biochemistry determinations. !16
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