Characterization and partial purification of a neutral protease from the serum of a patient with autosomal recessive pulmonary emphysema and cutis laxa.

Serum enzyme activity in 81 patients with various medical and dermatologic problems was determined with succinyl-(L-alanyl)3-p-nitroanilide as substrate. Values exceeding the limit of mean +/- 3 SD in healthy controls were detected in 16 patients. The highest activity, greater than 80 times the mean in the controls, was found in a 20-year-old patient with severe pulmonary emphysema and cutis laxa. The enzyme activity in the patient's serum was enhanced by Ca2+ and was inhibited by metal chelators but not by serine protease inhibitors. The pH optimum of the enzyme was 7.6. The enzyme was partially purified by gel filtration chromatography. Enzyme activity eluted in two major peaks with apparent molecular weights of greater than 10(7) daltons (peak I) and approximately 2.5 X 10(5) daltons (peak II). When compared with the elution patterns in the patient's mother and a healthy control, the elevated enzyme activity in the patient's serum was associated with peak I. The partially purified enzyme in peak I was not complexed with alpha 2-macroglobulin. The peak I enzyme was capable of degrading tropoelastin and a synthetic dinitrophenyl peptide at a glycyl-isoleucyl sequence, but not native or denatured collagen.