Plasma carboxypeptidase activity and intolerance to acetylsalicylic acid unimpaired CP-N activity in ASA-intolerant individuals.

Carboxypeptidase N (EC 3.4.17.3, arginine carboxypeptidase, kininase, anaphylatoxin inactivator) activity was determined in human sera with the method of Erdös by differential spectrometry at 254 nm and 37 degrees 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/1. The mean value in a pool of sera from 12 healthy pregnant women, 4,500 +/- 294 IU/1, 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/1, and those from 17 patients with chronic asthma or chronic urticaria and ASA intolerance 3,379 +/- 575 IU/1. 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/1.