Structure of Plasmic Degradation Products of Human Fibrinogen: FIBRINOPEPTIDE AND POLYPEPTIDE CHAIN ANALYSIS

Abstract

Direct determination of fibrinopeptides A and B in purified plasmic degradation products of human fibrinogen shows that fibrinogen and Fragments X and Y contain 2 moles of fibrinopeptide A per mole; Fragment E has approximately 0.3 mole of fibrinopeptide A per mole. Fibrinopeptide B is present in only trace amount in some Fragment X preparations and is absent from Fragments Y and E. Fragment D contains neither fibrinopeptide A nor B. These data and the results on molecular weight, carbohydrate content, and reactivity with thrombin of polypeptide chains of the purified degradation products were used to assign these chains to the Aα, Bβ, or γ chains of the original fibrinogen molecule. Fragment X has altered Aα chains with a molecular weight of 25,000, Bβ chains that are either intact (58,000) or cleaved at the NH2-terminal end (53,000), and γ chains that are either intact (48,000) or cleaved at the COOH-terminal end (40,000). Fragment Y has two distinct sets of polypeptide chains; the heavier ones are almost the same as those of the smallest Fragment X species. The lighter chains of Fragment Y are similar to those of Fragment E, which has three major components of 13,000, 8,000, and 10,000 assigned tentatively as Aα, Bβ, and γ fibrinogen chain remnants, respectively. The chains of Fragment D have been classified as a 13,000 molecular weight α chain remnant, a 42,000 β chain remnant and a heterogeneous group (39,000, 32,000, and 26,000) of γ chain remnants. The presence of 2 moles of fibrinopeptide A per mole of Fragment Y and the demonstration of the heavy and light sets of polypeptide chains in Fragment Y provide substantive evidence for its asymmetric structure.