Proposed model of MASP-1 mediated prothrombin cleavage.

There are two different pathways of prothrombin cleavage. MASP-1 cleaves first at R271, yielding prethrombin-2 which is subsequently cleaved at R393 to form the active species α-thrombinR393. When R393 is cleaved first, the active intermediate mIIR393 results. This intermediate is cleaved by MASP-1 (at R271) and itself (at R320) resulting in β-thrombin’ and mIIR393’, respectively. Further active species cannot be excluded. The small letters correspond to the nomenclature of the bands in Fig 2.