Arginine carboxypeptidase (CPR) in human plasma determined with sandwich ELISA

There are two types of carboxypeptidases present in human blood, carboxypep tidase N (CPN) and arginine carboxypeptidase (CPR), CPR is generated during coagulation from a precursor (proCPR) which can be converted to the active form by trypsin in vitro, Since it is difficult to distinguish the two typ es of carboxypeptidases in human blood by the measurement of enzyme activit y, we established a quantitative sandwich ELISA by which CPR can be quantit ated, The amount of CPR in plasma, fresh serum and heated serum were essent ially the same. Therefore the ELISA assay does not distinguish proCPR, acti vated CPR and inactivated CPR, With the ELISA method, CPR was quantitated i n plasma from fifty patients with rheumatoid arthritis and eleven patients with severe hepatitis as well as healthy individuals, The amount of CPR in plasma obtained from patients with rheumatoid arthritis was not found to be lower than that of normal subjects, Furthermore, the patients who suffered severe hepatitis and had very low levels of CPR-total were fatal, This sug gests that a decrease of CPR level might be a good indication of a patient' s prognosis to death by hepatitis.