Copyright 9 1997 by Humana Press Inc. All rights of any nature whatsoever reserved. 0273-2289/97/620203---0317511.00 Immobilization of Xanthine Oxidase and Its Use in the Quantitation of Hypoxanthine in Fish Muscle Tissue Extracts Using a Flow Injection Method DERRICK A. BALLADIN, *'1 DYER NARINESINGH, 2 VALERIE A. STOUTE, 3 AND T. T. NGO 4 1Chemistry Department, University of the West Indies, Cave Hill Campus, Barbados, WI; 2Chemistry Department, University of the West Indies, St. Augustine Campus, Trinidad, WI; and 3V.A.S. Consulting, New York, NY, 4AMDL, Tustin, CA ReceivedDecember 5, 1995; AcceptedJanuary4, 1996 ABSTRACT Fish muscle extracts (Scomberomorus-brasiliensis--carite) were ana- lyzed for their hypoxanthine content using a flow injection system incor- porating an immobilized xanthine oxidase bioreactor. The xanthine oxidase was immobilized under mild conditions to a 2-fluoro-1- methylpyridinium Fractogel support. The uric acid produced from the oxidation of hypoxanthine by the immobilized xanthine oxidase at pH 7.0 and 35~ was monitored at 290 nm. Hypoxanthine concentrations as low as 4.4 ~tmol/L can be detected. Up to 30 samples per hour can be ana- lyzed at a flow rate of 1 mL/min, using 150 gL sample volumes and a bioreactor dimension of 1.0 cm x 2.0 mm id. Recovery yields were between 92 and 99%. Both within day and between day precisions gave CVs < 5.00% (n = 30). Good correlation (r -- 0.998) is obtained when 78 fish samples were analyzed for their hypoxanthine content both by this FI method and a reference HPLC method. Index Entries: Immobilized xanthine oxidase; flow injection; hypox- anthine; fish muscle tissue. *Author to whom all correspondence and reprint requests should be addressed. Applied Biochemistry and Biotechnology 317 Voi. 62, 1997