A serum enzyme test to detect pulmonary capillary injury

Lung converting enzyme (LCE) was extracted from normal human lung obtained at autopsy. The specificity of the enzyme preparation was confirmed in vitro by incubation with Angiotensin I (AI) and paper chromatographic identification of reaction products. A method was developed for assay of the enzyme preparation in human serum using tritiated Angiotensin I (H-3A-I) as substrate. Enzyme activity is quantitated by scintillation counting the radioactive end product tritiated dipeptide histadylleucine (H-3His-leu). Serum from the authors and pooled serum from the hospital laboratory caused less than 3.5% conversion of H-3A-I to H-3His-leu. Serum from two patients with severe lung damage caused a maximum 20% conversion of H-3A-I to H-3His-leu. Percent conversion in these patients correlated with clinical and laboratory evidence of lung dysfunction.