Resolution of granules from rabbit heterophil leukocytes into distinct populations by zonal sedimentation.
Postnuclear supernates from homogenates of essentially pure rabbit heterophil leukocytes were fractionated by means of zonal differential centrifugation through a discontinuous sucrose gradient at various speeds. Three distinct groups of granules were characterized biochemically and morphologically. They were, in order of decreasing sedimentation coefficient: (a) Large, relatively dense granules, identified morphologically as the azurophil or primary granules, and containing essentially all of the myeloperoxidase activity of the preparations, about one-third of their lysozyme activity, and between 50 and 80% of their content in five acid hydrolases typically associated with lysosomes in other cells; (b) smaller, less dense granules, with the morphological appearance of the specific or secondary granules, and carrying most of the alkaline phosphatase and the remainder of the lysozyme activity of the preparations; (c) a second group of lysosome-like particles, associated with a morphologically heterogeneous fraction, and containing the remainder of the acid hydrolases, but little or no myeloperoxidase. When p-nitrophenyl phosphate was used instead of beta-glycerophosphate for the assay of acid phosphatase, only small proportions of the total activity accompanied the two main lysosomal bands, and considerable activity was found in a zone slightly retarded with respect to the slowly moving band of acid hydrolases.