An enzymatic method for the kinetic measurement of L-asparaginase activity and L-asparagine with an ammonia gas-sensing electrode

A simple kinetic method to assay L-asparaginase and L-asparagine with an ammonia gas-sensing electrode is described. The method is based upon the de-amination of L-asparagine by L-asparaginase from Escherichia coli, resulting in the production of ammonia. The initial rate (mV/min) of ammonia release is proportional to the activity of L-asparaginase and also to the concentration of L-asparagine in the presence of a large amount of the enzyme. Optimal temperature, buffer composition and pH for the assays are specified. L-Asparaginase was determined in the range of 0.4-1.6 U in a 0.1 ml sample; the recovery was 98.1-103.8% for 16 determinations and sigma n was 1.59. L-Asparagine was determined in the concentration range of 1 x 10(-4)--1 x 10(-3) M with sigma n-1 1.92. The method was applied to the determination of 1-5 x 10(-4) M asparagine added to human serum with sigma n-1 1.96 for 5 determinations.