THE EFFECT OF CHEMICAL MODIFICATION OF BASIC-AMINO-ACID RESIDUES ON THE ACTIVATION AND AMIDOLYTIC ACTIVITY OF HAGEMAN-FACTOR (FACTOR-XII)

Modification of arginyl residues of Hageman factor by phenylglyoxal hy drate inhibits activation of this clotting factor in a plasma-free sys tem, that is, in the absence of the other constituents of the contact activation system. Activation is also inhibited by alteration of the o ther two basic amino acid residues present, lysine and histidine. Chem ical modification of histidine and arginine residues does not inhibit the amidolytic activity of activated Hageman factor. In contrast, modi fication of amino group(s) in N-terminal and lysine residues inhibits activated Hageman factor. Thus, basic amino acid residues essential to the activation or activity of Hageman factor appear to be variably ac cessible to chemical modification.