Prothrombin Human Plasma. Prothrombin, Source: Human Plasma, Physical Form Description: In 20 mM Tris-HCl, 0.1 M NaCl pH 7.4, Molecular Weight: 72 kDa, Purity: greater than or equal to 95%, Storage Temperature: -80 deg C Synonyms: Coagulation factor II, Not For Use in Humans, Size: 1 mg