Platelet membrane glycoproteins IIb and IIIa (GPIIb and GPIIIa) constitute the fibrinogen receptor and are required for platelet aggregation. Glycoprotein IIb consists of 2 disulfide-linked subunits GPIIb (MW = 125,000) and GPII (MW= 23,000) while GPIIIa has only one polypeptide chain (MW= 108,000). GPIIbIIIa migrates on gels as follows: GPIIb 136,000 non-reduced and 125,000 reduced. GPIIIa is 97,000 non-reduced and 108,000 reduced. Protein concentration is determined via the Bradford method.