A Polyvalent Proteinase Inhibitor from Horse‐Blood‐Leucocyte Cytosol

Cytosol of horse blood polymorphonuclear leucocytes contains an inhibitor active against neutral proteinases from the granules of these cells and against chymotrypsin, elastases I and II from pig pancreas, but not against trypsin. A method has been elaborated to isolate and purify this inhibitor by means of salting out with ammonium sulphate (45---70% saturation), followed by chromatography and rechromatography on a column of DEAE-Sephadex A-50. The preparation obtained is homogeneous during polyacrylamide gel electrophoresis in the presence of 0.1% sodium dodecylsulphate after reduction with 2-mercaptoethanol. It is a thermolabile protein soluble at its isoelectric point (pH 5.38) and having a molecular weight of 35200 but aggregating in solutions of low ionic strength and irreversibly precipitating during dialysis at pH 4.0. The results obtained show the similarity of this inhibitor isolated from horse blood leucocyte cytosol to other inhibitors isolated from human or pig blood leucocytes.