 Of these, alpha granules are the most common.The term "alpha granules" is used to describe granules containing several growth factors.Contents include insulin-like growth factor 1, platelet-derived growth factors, TGFβ, platelet factor 4 (which is a heparin-binding chemokine) and other clotting proteins (such as thrombospondin, fibronectin, factor V, and von Willebrand factor).