Development of Enzyme-Linked Immunosorbent Assays for Diagnosis of Liver Diseases

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Urea cycle is composed of five enzymes, carbamylphosphate synthetase (CPS), ornithine transcarbamylase (OTC), argininosuccinate synthetase (AS), argininosuccinate lyase (AL) and arginase. All these enzymes are expressed most strongly in the liver. In addition to the liver, CPS and OTC are expressed moderately in the small intestine, and AS and AL are expressed moderately in the kidney. Among the five enzymes, CPS and OTC are mitochondrial, whereas AS,AL and arginase are cytosoloc . CPS consists 4-5% of total liver protein and other enzymes do 0.1-0.2%. We developed a sensitive enzyme-linked immunosorbent assay (ELISA) of OTC and showed that this system will and in diagnosing various liver diseases. In addition to previously prepared antibodies against OTC and CPS,we prepared antibodies against AS,AL and arginase. Using these antibodies, we analyzed intrahepatic localization of these enzymes. Among the five enzymes, CPS,AS,AL and arginase showed a strong peritortal to pericentral zonation, whereas OTC showed only a very weak zonation. These imformations will be important for interpretation of the ELISA data for the urea cycle enzymes in the plasma of patients.