第Ⅻ因子

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血液凝固の開始、線溶、ブラジキニンとアンギオテンシンの生成に関与する。
プレカリクレインは第Ⅻ因子により切断されカリクレインとなる。カリクレインはトリプシンとともに第Ⅻ因子を活性化する。第Ⅻ因子は第Ⅺ因子を活性化する。
Factor XII is a serum glycoprotein that participates in the initiation of blood coagulation, fibrinolysis, and the generation of bradykinin and angiotensin. Prekallikrein is cleaved by factor XII to form kallikrein, which then cleaves factor XII first to alpha-factor XIIa and then trypsin cleaves it to beta-factor XIIa. Alpha-factor XIIa activates factor XI to factor XIa.

Catalytic activity

Selective cleavage of Arg-|-Ile bonds in factor VII to form factor VIIa and factor XI to form factor XIa.

Post-translational modification

Factor XII is activated by kallikrein in alpha-factor XIIa, which is further converted by trypsin into beta-factor XIIa. Alpha-factor XIIa is composed of an NH2-terminal heavy chain, called coagulation factor XIIa heavy chain, and a COOH-terminal light chain, called coagulation factor XIIa light chain, connected by a disulfide bond. Beta-factor XIIa is composed of 2 chains linked by a disulfide bond, an N-terminal nonapeptide, called beta-factor XIIa part 1, and coagulation factor XIIa light chain, also known in this context as beta-factor XIIa part 2.
O- and N-glycosylated. The O-linked polysaccharides were not identified, but are probably the mucin type linked to GalNAc.
カリクレインにより活性化第Ⅻ因子α（Ｎ末端側の重鎖）とc末端側の第Ⅻ因子軽鎖に分かれる。さらにトリプシンにより活性化第Ⅻ因子βとなる。