SUBCELLULAR-LOCALIZATION OF HUMAN-PLATELET ANTIHEPARIN PROTEINS

The distribution of two platelet antiheparin proteins, platelet factor 4 (PF4) and low affinity platelet factor 4 (LA-PF4) measured by radioimmunoassays and of antiheparin activity measured by a chromogenic assay, was determined in human platelet granule fractions separated by sucrose density centrifugation. Subcellular fractions were characterized by the levels of serotonin (dense granule marker) and β-N-acetylglucosaminidase (lysosomal enzyme marker). PF4 and LA-PF4 antigens and antiheparin activity showed an identical distribution pattern with the highest specific activities occurring in a fraction lighter than that containing serotonin. The fraction with the highest specific activity of β-N-acetylglucosaminidase was observed at a lighter sucrose density than the fraction most enriched in platelet antiheparin proteins. These results indicate that PF4, LA-PF4 and heparin-neutralizing activity are located in the same granule fraction (α-granules) which is different from both the serotonin and the β-N-acetylglucosaminidase-containing fractions. The PF4 and LA-PF4 amounted to 13% of the total proteins of α-granules as determined by radioimmunoassay and SDS polyacrylamide gel densitometric scanning. © 1979.