Highly purified fibrinogen-fibrin related antigen (FR-antigen) was isolated with good recovery from 1.0--2.0 ml of human plasma, by immuno-affinity chromatography with antibody specific for fibrinogen and fibrin, and plasmin degradation products X, Y, D and D-D dimer. In FR-antigen from defibrinating patients there was evidence for thrombin activity alone (mainly disseminated cancer) or both plasmin and thrombin (mainly abruptio placentae). Thus, the molar ratio of N-terminal Gly-Tyr in the FR-antigen of 18 of 20 patients strongly suggested thrombin activity (95th percentile). In addition, sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE) on unreduced samples frequently showed bands similar in mol wt to fragments X, Y and D, and in the reduced samples A alpha and B beta chain degradation, both indicating plasmin activity. 'N-terminal beta chain Ala' was elevated in the antigen of four of 20 patients, also suggesting plasmin activity (99th percentile). Combined thrombin, plasmin and factor-XIII activity, as shown with high levels of serum FR-antigen (greater than 10 mg/dl). In some defibrinating patients, especially those with disseminated cancer, heterogeneity of unreduced FR-antigen and A alpha chain degradation, both indicators of mild plasmin-like activity which are commonly seen in normals, were absent.

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The N-terminal sequences of the separated polypeptide chains of biliproteins isolated from several Cyanophyta, Rhodophyta, and Cryptophyta have been determined. The portions of the sequences determined for the alpha (fast) chain of C-phycocyanin from both procaryotic and eucaryotic cells are extremely conservative. Methionine is the N-terminal amino acid in most of the species studied. The N-terminus and subsequent sequence of phycoerythrin alpha chains are almost identical with those of the C-phycocyanin alpha chain. The beta (slow) chain of C-phycocyanin is also rather conservative in amino acid substitution but has more variation than the alpha chain. The variations are consistent with single base changes in codons and conserve the size and functional characteristics of the amino acid. The sequence homologies are consistent with the phylogenetic relationship between Cyanophyta and the chloroplast of Rhodophyta. There are no other reported sequences of polypeptide chains of the same or related proteins from such different strains of microorganisms that show such close sequence homology.

Fibrinogen-fibrin-related antigen (FR antigen) was isolated from as little as 1 ml of human plasma by immuno-affinity chromatography with agarose-bound antibody to human fibrinogen. N-terminal analysis was performed to determine the nature and extent of proteolytic degradation of the FR antigen in patients with disseminated intravascular coagulation and in normal subjects. Thrombin cleavage of the A- and B-peptides from fibrinogen in vitro was monitored by the appearance of N-terminal glycine, and an increase in glycine was shown in the FR antigen of patients with disseminated intravascular coagulation. As plasmin progressively degraded fibrinogen, increases in N-terminal alanine, aspartic acid and lysine were observed, corresponding to the known plasmin-cleavage points of fibrinogen; increases in these N-terminal amino acids were also found in the patients' FR antigen. Thrombin treatment in vitro was used to remove fibrinopeptide A (N-terminal alanine) from the samples and to reflect specifically the N-terminal alanine at the plasmin-cleavage point (Arg-42-Ala-43) of the B beta-chain on assay; this alanine was increased progressively in the FR antigen of a patient during urokinase therapy, and was high in other patients when the FR antigen was examined by this procedure.

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