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Arginine carboxypeptidase (CPR) is a novel carboxypeptidase which was first described by Campbell and Okada. CPR is generated from a stable precursor of CPR (proCPR) during coagulation or under other circumstances and is promptly inactivated at 37 C. Therefore, it is not easy to determine CPR in blood samples. Since proCPR can be separated from the other basic carboxypeptidase (carboxypeptidase N; CPN) by passing plasma through DEAE gel, we have established a method to determine the amount of proCPR after converting it to active CPR by trypsin treatment. We first separated the proCPR from CPN using a filter cup tube (FC tube) packed with DEAE Sephadex, and measured activity after conversion of the enzyme to its active form using trypsin. With this method, no significant decrease in proCPR was noted in the plasma of patients including those with rheumatoid arthritis (RA), although CPR activity in fresh sera has been reported to be decreased. This discrepancy suggests that proCPR is not depleted in most patient sera, but that the level of activity of the enzyme which converts proCPR into active CPR may be compromised in RA patients.

Hemoglobin extracted from human placentas could be used as the basis of blood substitutes provided it could be prepared on a large scale with appropriate oxygen-binding properties. Unfortunately, the industrial conditions under which it is extracted, produce hemoglobin with high oxygen affinity and which is no longer influenced by the classical effectors. These characteristics were shown to be caused by a degradation of the α-chain brought by an arginine carboxypeptidase present in the placental tissues and leading to the disappearance of the C-terminal arginine residue. This carboxypeptidase which is released from the tissues during the proces of crushing the frozen placentas, degrades the protein during the chromatographic purification procedure. The addition of an inhibitor of this carboxypeptidase (for example, arginine) as soon as the placentas are thawed and during the chromatographic process, makes it possible to obtain placental hemoglobin with oxygen-binding properties quite similar to those of HbA prepared from peripheral venous blood.

Carboxypeptidase N (EC 3.4.17.3, arginine carboxypeptidase, kininase, anaphylatoxin inactiva-tor) activity was determined in human sera with the method of Erdös by differential spectrometry at 254 nm and 37°C, using hippuryl-L-argininic acid (HLAa) as a substrate. Day-to-day imprecision (CV) of the assay was 6.5%. The reference value, as determined in 15 healthy blood donors, was 3,082 ± 432 IU/l. The mean value in a pool of sera from 12 healthy pregnant women, 4,500 ± 294 IU/l, was higher, in accordance with earlier findings by Erdös et al. Sera from 53 patients with chronic asthma or chronic urticaria, without known acetylsalicylic acid (ASA) intolerance, gave the mean value of 3,583 ± 768 IU/l, and those from 17 patients with chronic asthma or chronic urticaria and ASA intolerance 3,379 ± 575 IU/l. Thus, the carboxypeptidase-N activity in the blood of ASA-intolerant asthmatics and urticaria patients was unimpaired. A 16-year-old boy with asthma and without ASA intolerance showed an unusually low value of 2,056 IU/l.