Aα 16 Arg→His substitutions are common forms of congenital dysfibrinogenemias. Clinical manifestations range from asymptomatic to moderate hemorrhagic tendencies. Biochemical characterization of one such heterozygotic individual (Fibrinogen Louisville, Galanakis, etal. Ann NY Acad Sci 408:644,1983) indicated that only homodimeric fibrinogen molecules (i.e., containing either normal or abnormal Aα chains) were present. We isolated fibrinogen from the plasma of a 23 year old patient with a history of easy bruising and several recent moderate to severe bleeding episodes. Coagulability with reptilase was 677 (65-70%; n=5) whereas with thrombin (Ha) it approached 100%, depending directly upon the time of incubation with enzyme. HPLC analysis of Ila-induced fibrinopeptide release demonstrated the presence of an abnormal A-peptide (A*), amounting to 50% of the total, which was released more slowly than the normal A-peptide (A). Amino acid analysis of A* demonstrated the absence of Arg and the presence of His. Carboxypeptidase digestion confirmed the structure of A* as Aα 16 Arg-→ His. The clot and the soluble clot liquor resulting from reptilase treatment were separated and each was then further treated with Ilato release A*. HPLC analysis indicated that 31% of the total A* present in the sample was associated with the reptilase clot and 697 remained in the clot liquor. This distribution of A* suggests that Fibrinogen Birmingham, unlike Fibrinogen Louisville, contains heterodimeric molecules that are incorporated into the reptilase clottable fraction. This finding is consistent with a process of random hepatic assembly of dimeric fibrinogen molecules in a heterozygotic individual.
Biochemical Characterization of Aspergillus fumigatus AroH, a Putative Aromatic Amino Acid Aminotransferase
