Neutral elastolytic proteinase from canine leucocytes. Purification and characterization.

1. A neutral proteinase (EC 3.4.-.-) with elastolytic activity was isolated from canine bloodstream leucocytes, and purified to apparent homogeneity by a two-step procedure consisting of DEAE-Sephadex chromatography and molecular sieving on Sephadex G-75. 2. The molecular weight of the enzyme was 23 500, and the absorbance (A1%1cm) at 282 nm was 6.1. Amino acid analysis showed high content of glycine, aspartic acid, and valine, and low proportion of methionine, lysine and histidine as well as the absence of tyrosine in the enzyme molecule. 3. The proteinase was active against several protein substrates as well as towards N-t-butyloxycarbonyl-L-alanine p-nitrophenyl ester, N-acetyl-L-alanyl-tyrosine ethyl ester. 4. The enzyme was inactivated by diisopropylfluorophosphate, N-acetyl-L-alanyl-L-alanyl-L-alanine chloromethyl ketone, and N-p-tosyl-L-phenylalanine chloromethyl ketone. Inhibition by some natural proteinase inhibitors was also noted.