Characterization of PIG Platelet Granule Proteins
Platelet granules contain glycoproteins similar to those found in platelet membranes (Hagen et al , BBA , 445, 21 4 , 1 976 ). Pig platelet granule fractions enriched in mitochondria, α-granules or dense granules were analyzed by SDS Polyacrylamide gel electrophoresis to determine if there are differences among the organelles. In a reduced system (5Ϊ OTT) the proteins of the ï-granules and dense granules showed staining patterns with Coomassie blue that were distinctly different from whole platelets, isolated membranes or mitochondria. In the granules about 10 to 12 bands with less mobility than actin were visualized. Staining with PAS was obtained in bands with apparent molecular weights of 250, 225, 185, 170, 150, 120, 55, 4B and 40 K. The 185 K band appeared to be the same as “thrombin sensitive protein”. The mobility of the 55 and 48 K hands were identical with the B (B) and γ-bands of bovine fibrinogen. The PAS staining of the granule components was more intense than that of whole platelets for the same amount of protein, indicating that granule membranes may be as rich in glycoproteins as external plasma membranes. With both PAS and Coomassie blue, the a-granule and dense granule staining patterns were almost identical. This observation may be relevant to recent studies which showed that both granule types exhibited similar release characteristics, suggesting that they share a common release mechanism. NIH-JSPHS Grant No. 14217