Plasma prekallikrein is a
glycoprotein that participates in the
surface-dependent activation of blood coagulation,
fibrinolysis,
kinin generation and
inflammation. It is synthesized in the liver and secreted into the blood as a single
polypeptide chain. Plasma prekallikrein is converted to plasma kallikrein by factor XIIa by the cleavage of an internal Arg-
Ile bond. Plasma kallikrein therefore is composed of a heavy chain and a light chain held together by a
disulfide bond. The heavy chain originates from the
amino-terminal end of the
zymogen and contains 4
tandem repeats of 90 or 91 amino acids. Each repeat harbors a novel structure called the
apple domain. The heavy chain is required for the surface-dependent
pro-coagulant activity of plasma kallikrein. The light chain contains the
active site or catalytic domain of the enzyme and is
homologous to the trypsin family of
serine proteases. Plasma prekallikrein deficiency causes a prolonged
activated partial thromboplastin time in patients. == Interactions ==