The neutrophil glycoprotein Mol is an integral membrane protein of plasma membranes and specific granules

The glycoprotein Mol has previously been demonstrated to be on the cell surface and in the specific granule fraction of neutrophils and to be translocated to the cell surface during degranulation. It is not known, however, whether Mol is an integral membrane protein or a soluble, intragranular constituent loosely associated with the specific granule membrane. Purified neutrophils were disrupted by nitrogen cavitation and separated on Percoll density gradients into four fractions enriched for azurophilic granules, specific granules, plasma membrane, and cytosol, respectively. The glycoproteins in these fractions were labeled with ³H-borohydride reduction, extracted with Triton X-114, and immunoprecipitated with 60.3, an anti-Mol monoclonal antibody. Mol was detected only in the specific granule and plasma membrane fractions and partitioned exclusively into the detergent-rich fraction consistent with Mol being an integral membrane protein. In addition, treatment of specific granule membranes with a high salt, high urea buffer to remove adsorbed or peripheral proteins failed to dissociate Mol. These data support the hypothesis that Mol is an integral membrane protein of plasma and specific granule membranes in human neutrophils.