Studies of the advanced stages of the plasmin and trypsin digestion of bovine fibrinogen

The advanced stages of the digestion of bovine fibrinogen by trypsin and by plasmin have been investigated. The fragmentation of the molecule has a nearly identical course with the two enzymes, however, plasmin accomplishes the same result by cleaving only 1/2 to 2/3 as many bonds as trypsin. The advanced digestion can be divided into two stages. First, fragment D formed during the early part of the reaction is transformed into a number of successively lower molecular weight subspecies, with accompanying liberation of peptides of lower than 16,000 molecular weight. Second, in a very slow process, the products of the preceding stage are broken up into a homogeneous mixture of fragments encompassing a wide range of molecular weights. Fragment E remains unchanged during the whole process.