Uric acid is a main electron donor to peroxidases in human blood plasma.

BACKGROUND: Peroxidases are widely distributed and have been isolated from many higher-order plants, animal tissues, yeast and microorganisms. During measurements of peroxidase activities in samples of human plasma, we noticed the presence of a compound in the plasma which was interfering with the peroxidase assay. In this paper we describe the purification and characterization of this factor, which was identified as uric acid. MATERIAL/METHODS: The procedure used to purify uric acid from plasma involved ultra-filtration of the plasma, heat denaturation, DEAE-cellulose chromatography, and high performance liquid chromatography. The lyophilized powder was tested for homogeneity using an HPLC apparatus and capillary electrophoresis. Genuine uric acid samples were used for comparison. RESULTS: The compound obtained by the above-reported purification procedure was identified as uric acid by spectrophotometric analysis through comparison with genuine uric acid samples. Spectrophotometric measurements indicated that uric acid was degraded by HRP in the presence of H2O2. CONCLUSIONS: The experimental procedures described above allowed us to isolate and identify uric acid as the component in human plasma that acts as a true substrate for peroxidases.