Differential determination of human liver and pancreas dipeptidase activities by using specific antibody-conjugated paper disks.

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Abstract
A new method was developed for the determination of liver and pancreas dipeptidase activities in serum by using specific antibody-conjugated paper disks. The immunoreaction between the antibody-conjugated paper disks and the dipeptidases reached a plateau within 7h at 4°C, and no dipeptidase activity was detected in the reaction medium thereagter. The calibration curves obtained by the proposed method passed through the origin and were linear in the ranges of 0-200 ng of liver dipeptidase and 0-37.5 ng of pancreas dipeptidase. The bound enzymes from human liver and pancreas had higher Km values and lower Vmax values toward L-Leu-L-Leu than those of the corresponding free enzymes. However, with L-Ala-L-Ala as a substrate, the Km and Vmax values of the pancreas dipeptidase bound on the paper disk and the free enzyme were almost the same. The recoveries of added liver and pancreas dipeptidases from serum were more than 96%. The proposed method showed a good precision. The normal value of liver dipeptidase activity in serum was 1.62±0.40 I.U./l of serum (mean±S.D.). The activities were elevated in acute hepatitis (18.7±18.2 I.U./l, p<0.001 vs. normal) and liver cancer (12.3±12.9 I.U./l, p<0.001). The normal value of pancreas dipeptidase activity in serum was 0.74±0.99 I.U./l of serum. The activities were remarkably elevated in pancreatic cancer (5.22±2.68 I.U./l, p<0.001) and acute pancreatitis (4.82±2.84 I.U./l, p<0.001). These results suggest that this method may be useful in the clinical diagnosis of hepatic and pancreatic diseases.

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