1. Anti-elastase function in sputum sol-phase from patients with α 1 -proteinase inhibitor (α 1 PI) deficiency was compared with sol-phase from patients with cigarette smoke-induced bronchitis and emphysema. 2. Both α 1 PI (2 P < 0.01) and anti-leucoprotease (ALP) (2 P < 0.01) concentrations were lower in sol-phase from the α 1 PI-deficient group, although α 2 -macroglobulin (α 2 M) levels were similar. 3. There was no difference in α 1 PI function between the two groups, but the inhibitor was only ≃ 30% active. 4. The absolute neutrophil elastase (NE) inhibitory capacity was similar in both groups (median 185 μg of NE inhibited/ml of sputum, range 80–480, for the α 1 PI-deficient group; median 175, range 80–300, for the bronchitic group). A substantial proportion of NE inhibition in secretions could not be accounted for by the amount of α 1 PI, ALP and α 2 M present (median 74.8%, range 43.2–97.4, for α 1 PI-deficient sol-phase; median 50.0%, range 0–80.8, for bronchitic sol-phase). 5. Gel filtration of sol-phase demonstrated the presence of NE inhibition in the low molecular weight fractions which was markedly sensitive to changes in substrate concentration and ionic strength, in contrast to purified α 1 PI and ALP. 6. Sputum sol-phase from both groups failed to prevent hydrolysis of elastin–fluorescein or succinyltrialanyl- p -nitroanilide by NE completely during prolonged incubation in the presence of an excess of functional inhibitors. This was more apparent in secretions from subjects with α 1 PI deficiency and may explain why such patients have a more rapidly progressive form of emphysema.

1. Two-dimensional immunoelectrophoresis and conventional sodium dodecyl sulphate-polyacryl-amide gel electrophoresis was performed on various mixtures of purified α 1 -antitrypsin (α 1 AT) and leucocyte elastase (LE). 2. The results confirm that α 1 AT inhibits LE by the formation of enzyme-inhibitor complexes demonstrable by both techniques. 3. The complexes break down with time and are not affected by pH in the presence of excess α 1 AT. However, the breakdown is more rapid in the presence of excess enzyme only at pH values where LE remains active. The resultant products of the complex breakdown include inactivated LE and α 1 AT that has undergone limited proteolysis. 4. It is concluded that the presence or absence of α 1 AT-enzyme complexes as demonstrated by two-dimensional immunoelectrophoresis must be interpreted with caution when studying α 1 AT function in lung secretions. The absence of such complexes does not mean that previous interaction with enzyme has not occurred, thereby accounting for a reduction in α 1 AT inhibitory capacity.

1. The quantification of α 1 -antitrypsin (α 1 AT) by standard immunological techniques is altered by interaction of the protein with leucocyte elastase. 2. The results obtained for α 1 -antitrypsinleucocyte elastase mixtures in the presence of a functional excess of the inhibitor were relatively accurate for the first 6 h. However, continued incubation for more than 24 h led to a major over-estimation of the α 1 AT as the result of breakdown of the enzyme-inhibitor complex releasing a partially proteolysed form of the inhibitor. 3. In the presence of excess enzyme up to a twofold overestimation of α 1 AT occurred within 1 h and the degree of overestimation increased with time (up to threefold at 24 h). This was eventually associated with the presence of only a partially proteolysed form of α 1 AT (mol wt. ⋍ 50000). 4. Different results for each sample were obtained when different polyclonal antisera were used to quantify the α 1 AT. 5. Complete inactivation of α 1 AT by oxidation resulted in little change in the immunological quantification of the protein. However, further addition of H 2 O 2 led to a progressive underestimation of the α 1 AT. 6. The effect of physicochemical alteration on the immunological quantification of α 1 AT by different antisera should be borne in mind for all studies assessing this protein in lung secretions.