PROTEIN BINDING OF AZO DYES BY TISSUE HOMOGENATES

In the colorimetric estimation of sulfatase activity in tissues based upon the conversion of 6-benzoyl-2-naphthol, liberated by enzymatic hydrolysis, to an azo dye by exposure to tetrazotized diorthoanisidine, a substantial fraction of the dye is adsorbed by tissue homogenate. This also occurs with protein fractions. The fraction of total dye adsorbed increases with protein or homogenate concentration and varies with the type of protein or homogenate used. The adsorption by protein conforms empirically to a general theoretic equation for the binding of azo dyes to protein. Azo dyes derived from 6-bromo- or 6-benzoyl-2-naphthol were adsorbed more extensively than the dyes derived from 1- or 2-naphthol.