Esterases in Human Neutrophil Granulocytes: Evidence for their Protease Nature

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Abstract
Summary. The nature of the esterases localized in granules of human neutrophil granulocytes has been investigated. The esterases of the granule fraction were fractionated first by selective solubilization of the granule proteins with 0.15 M‐NaCl and subsequently by gel filtration of the dissolved proteins on Sephadex G‐75. The chymotrypsin‐like activity of the granule fractions was insoluble in 0.15 M‐NaCI. Part of the granule esterase activity is known to be due to this chymotrypsin‐like enzyme. The soluble esterase activity of the granule fraction could be attributed to proteases as well. Two peaks of proteolytic activity on casein at pH 8.0 were obtained by gel filtration. The peak eluted first from the Sephadex G‐75 column contained two esterase proteins with a molecular weight of about 70000. The second protease peak contained the elastase‐like activity in addition to other proteases. A molecular weight of about 33000 was estimated for these proteins. Acrylamidegel electrophoresis of this fraction revealed a pattern of esterase bands. No esterase bands were demonstrable on the gel electrophoretograms given by fractions without proteolytic activity.