Prekallikrein
Prekallikrein, also known as Fletcher factor, is an 85,000 Mr serine protease that complexes with high-molecular-weight kininogen. PK is the precursor of plasma kallikrein, which is a serine protease that activates kinins. PK is cleaved to produce kallikrein by activated Factor XII.
Structure
Prekallikrein is homologous to factor XI, and similarly consists of four apple domains and a fifth, catalytic serine protease domain. The four apple domains create a disk-like platform around the base of the catalytic domain.However, unlike factor XI, prekallikrein does not form dimers.
Prekallikrein is activated to form kallikrein by factor XII cleavage of a bond homologous to the corresponding bond cleaved during factor XI activation.
Prekallikrein deficiency
Hereditary deficiencies in PK are very rare. They can cause a prolonged APTT, which can be corrected by incubation of the patient’s plasma.Deficiencies in PK can also be acquired due to some disease states, such as angioedema, infection, DIC, and sickle-cell disease.
Although most cases of prekallikrein deficiency are asymptomatic, a few reports link severe prekallikrein deficiency with thrombotic phenomena and recurrent pregnancy loss. More recently, a case of prekallikrein deficiency was shown to be associated with severe mucosal bleeding.