Identification of precursor of phagocytosis-stimulating factor in guinea pig polymorphonuclear neutrophils.

A precursor of phagocytosis-stimulating factor (PSF) was identified by immunoblot assay with purified anti-PSF antibodies. The purified anti-PSF antibodies recognized not only the PSF with a molecular weight of 16,000 (16K) but also the 36K protein with a pI of 6.5 in the granule fraction of polymorphonuclear neutrophils, indicating that this 36K protein has an antigenic determinant common to PSF. In addition, the appearance of the PSF during phagocytosis by polymorphonuclear neutrophils was closely correlated to the decrease of the 36K protein. These results suggest that the 36K protein is the precursor of PSF which is converted to biologically active PSF in the granules during phagocytosis.