Consideration of the optimum pH for the analysis of serum p-phenylenediamine oxidase activity in thoroughbred horses.

The optimum pH for the measurement of serum p-phenylenediamine oxidase (Ox) activity was given (pH 6.6), and the relationship between serum ceruloplasmin (Cp) concentration and its Ox activity was established in healthy adult horses. In adult horses, serum antigenic Cp concentrations were measured by the single radial immunodiffusion (SRID) method with the affinity-purified antibody to equine plasma Cp and compared with its Ox activity. Efficient co-relation between Cp concentration and Ox activity in the sera (r = 0.93) and its Ox/Cp ratio were given. These results might contribute to the calculation of antigenic Cp concentration from its Ox activity, the analysis of holo-Cp content in serum, and the research for copper metabolism in thoroughbred horses.