Specific and azurophilic granules from rabbit polymorphonuclear leukocytes. II. Cell surface localization of granule membrane and content proteins before and after degranulation

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Abstract
The compositional relationship between the cell surface of rabbit polymorphonuclear leukocytes (PMN) and the membranes of PMN cytoplasmic granules was investigated. Heterophilic PMN obtained from peritoneal exudates contained 13 cell surface polypeptides ranging in MW from 220,000-12,000 daltons as determined by lactoperoxidase-catalyzed protein iodination and gel electrophoresis. Of these, 4 polypeptides comigrated with proteins identified as the major constituents of specific (SpG) and azurophilic (AzG) granule membranes. The most notable of these were cell surface proteins of 145,000 and 96,000 daltons that comigrated with SpG membrane proteins and a 48,000-dalton protein that was also a major component of AzG membranes. Also, 4 iodinated cell surface proteins comigrated with proteins identified as granule content proteins released from PMN during exocytosis. Extensive washing did not remove these proteins from the cell surface. Iodination of PMN after the release of SpG and AzG contents by Ca ionophore-induced exocytosis revealed that there was not a dramatic qualitative change in the proteins on the cell surface. Instead, there were large, quantitative increases in the relative amounts of 125I that were incorporated into several preexisting cell surface proteins; all of these cell surface proteins comigrated as a set with those polypeptides identified as either granule membrane or content proteins. Although nearly all of the major polypeptides of SpG and AzG had counterparts on the cell surface of freshly isolated peritoneal exudate PMN, there were several polypeptides that were unique to the cell surface. Thus, the PMN has at least 3 membrane compartments with strikingly different protein compositions.