Heterogeneity of granules of murine cytolytic T lymphocytes. Isolation of a homogeneous population of dense granules.

A separation procedure based on Percoll gradient centrifugation is described here that allows enrichment for two main populations of granules, with average densities of 1.05 and 1.1 g/ml. The heavy-density granules, which comprise 5-20% of the total amount of membrane-lytic activity, are morphologically and biochemically more homogeneous than the light-density granules, which are contaminated with other subcellular organelles. A trypsin-like serine esterase activity, used in the past as a granule marker, was mainly found in the free cytosol and in the light-density fractions, while a small portion of this activity was associated with the heavy-density fractions. This enzyme marker is therefore not exclusively associated with granules and should not be used as the only granule marker.