Homospecific activity, an immunologic index of enzyme homogeneity: Changes during the purification of dopamine-β-hydroxylase

The ratio of enzymatic activity to homologous enzyme protein (measured immunologically) can be used as a sensitive index of enzyme homogeneity. The name homospecific activity is proposed for this parameter (units of enzyme activity per mg of antigen). Measurements of homospecific activity allowed detection of inactive forms of dopamine-β-hydroxylase which accumulated during some purification procedures and which were not separable from active enzyme by standard analytical procedures. Homospecific activity is proposed as a routine index of homogeneity during enzyme purification.