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Carboxypeptidase N is a serum metalloenzyme that inactivates C3a, C4a, C5a, bradykinin, kalladin, and fibrinopeptides. Of 172 sera from patients with chronic urticaria or angioedema, one had a remarkably depressed carboxypeptidase N level (21% of normal). Of sera from 103 patients with other diseases, elevated levels were observed in cases of neoplasms, and one abnormally low value was detected in a patient with cirrhosis. The patient with a remarkably low carboxypeptidase N level was a 65-year-old man with an 11-year history of episodic angioedema occurring about 40 times per year. Inactivation of C3a and lysyl-bradykinin by his serum was markedly prolonged. Plasma histamine was elevated during attacks, but serotonin and kinin activity were not. The proband's sister had an equally depressed serum carboxypeptidase N level, and studies of other family members suggested an autosomal recessive inheritance of the enzyme deficiency.

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