A radiometric assay of copper binding in biological fluids and its application to alimentary secretions in normal subjects and Wilson's disease

A simple radiometric assay for the determination of copper binding by synthetic chelating agents and complex biological fluids has been developed. The assay makes use of the fact that most ionic copper compounds are insoluble at pH 8.0, whereas most copper—chelate compounds resist hydrolysis and remain soluble at this pH. The assay procedure has been described and the linearity, sensitivity and precision of the method determined for EDTA and l-histidine. Application of the procedure to saliva, gastric juice, duodenal aspirate and bile from normal persons demonstrated in each the presence of copper binding components which form soluble complexes under the alkaline conditions imposed in vitro. The problems inherent in quantitation of values from biological fluids are considered, especially in relation to gall bladder bile which bound greater amounts of copper than the other intestinal secretions examined. The values obtained from patients with Wilson's disease were the same as observed in normal subjects, although samples of bile were unavailable for assay. It is proposed that the endogenous ligands in gastrointestinal secretions may be involved in the control of mucosal uptake of dietary copper.