Ž . Bioelectrochemistry and Bioenergetics 44 1998 201–208 Comparison of electrochemical and enzymic oxidation of 1,3-dimethyluric acid Rajendra N. Goyal ) , Naveen K. Singhal Department of Chemistry, UniÕersity of Roorkee, Roorkee, 247 667, India Received 6 June 1997; received in revised form 22 September 1997; accepted 24 September 1997 Abstract Electrochemical oxidation of 1,3-dimethyluric acid has been studied in phosphate buffers of pH 2.3–10.3 at pyrolytic graphite electrode. The conjugate base has been found as the electroactive species and a single well-defined oxidation peak was observed. The presence of methyl groups have been found to shift E of uric acid towards less positive potential by 30–40 mV. The products of p electrooxidation were separated by HPLC at pH 3.0 and were characterized as 1,3-dimethylalloxan and urea. At pH 7.0, the major product Ž . was 5-hydroxyhydantoin-5- N-methyl carboxamide. The spectral studies during enzymic oxidation of 1,3-dimethyluric acid generated UV-absorbing intermediate similar to electrooxidation and the rate of decay was found to be same in both the cases. The electrochemical and enzymic oxidations appear to proceed by an identical mechanism. q 1998 Elsevier Science S.A. Keywords: Electrooxidation; Enzymic oxidation; 1,3-dimethyluric acid 1. Introduction The purine bases particularly xanthine, hypoxanthine and uric acid are measured in body fluids to provide wx information on intracellular nucleotides 1. 1,3-Dial- kylpurines on the other hand inhibit many of the phar- macological and physiological effects of adenosine particu- larly cardiac depressive and hypotensive by acting as competitive antagonists at A1- and A2-adenosine receptor w x subtypes 2,3 . In recent years mismatches of purines and pyrimidines in DNA duplexes have been reported to have wx disastrous effects on an organism 4 . The electrochemical studies have been found useful in providing information about biological reaction pathways. For example a key intermediate in the redox activation of mitomycin C, a powerful antitumor agent that alkylate DNA and RNA has wx been studied by using electrochemical studies 5 . The applications of electrochemistry for the elucidation of bio- logical redox mechanisms have been highlighted in a wx recent review 6 . In view of the importance of purines in biological systems, an attempt has been made in the pre- sent studies to elucidate electrochemical and enzymic oxi- Ž. dation of a dialkylpurine, viz., 1,3-dimethyluric acid I. ) Corresponding author. The electrochemical oxidation studies on purines and wx wx indoles by Dryhurst 7 , Wrona and Dryhurst 8 and wx Adams 9 and of phenothiazine drugs by Neptune and w x McCreery 10,11 supported the long held contention that electrochemical studies provide uniquely invaluable in- sights into the complex enzymic mechanism of biomolecules. It was concluded on the basis of voltammetric, con- trolled potential electrolysis and spectral studies that elec- trochemical and enzymic oxidation of 1,3-dimethyluric acid proceed by identical mechanism and thus the elec- trode surface of pyrolytic graphite electrode appear to act like an active site of the enzyme used. 2. Experimental details 1,3-dimethyluric acid was obtained from Aldrich Chem- Ž . ical, USA. The enzyme peroxidase type VIII R s 3.4 z isolated from horseradish was a product of Sigma, USA. Catalase used to stop enzymic oxidation was obtained 0302-4598r98r$19.00 q 1998 Elsevier Science S.A. All rights reserved.