catalytic activity:Cleaves selectively Arg-|-Xaa and Lys-|-Xaa bonds, including Lys-|-Arg and Arg-|-Ser bonds in (human) kininogen to release bradykinin.,disease:Defects in KLKB1 are the cause of prekallikrein deficiency (PKK deficiency) [MIM:612423]; also called Fletcher factor deficiency. This disorder is a blood coagulation defect.,function:The enzyme cleaves Lys-Arg and Arg-Ser bonds. It activates, in a reciprocal reaction, factor XII after its binding to a negatively charged surface. It also releases bradykinin from HMW kininogen and may also play a role in the renin-angiotensin system by converting prorenin into renin.,similarity:Belongs to the peptidase S1 family.,similarity:Belongs to the peptidase S1 family. Plasma kallikrein subfamily.,similarity:Contains 1 peptidase S1 domain.,similarity:Contains 4 apple domains.,subunit:The zymogen is activated by factor XIIa, which cleaves the molecule into a light chain, which contains the active site, and a heavy chain, which associates with HMW kininogen. These chains are linked by one or more disulfide bonds.,