Purification and characterization of human bronchial proteinase inhibitor

We describe a purification procedure for the human bronchial proteinase inhibitor which involves trichloroacetic acid precipitation of sputum followed by ion-exchange and gel filtration chromatography. The inhibitor shows a major band on sodium dodecyl sulfate-polyacrylamide gel electrophoresis, but exhibits microheterogeneity on high-resolution chromatography. It has a molecular mass of 15.5–16 kDa as determined by electrophoresis and gel filtration and is 90% active against leukocyte elastase. The amino acid sequence of the N-terminal portion of the inhibitor was determined and was found to be identical (through 29 amino acids) to that recently reported for the human seminal plasma proteinase inhibitor I.