Factor X Human Plasma. Factor X, Source: Human Plasma, Physical Form Description: In 20 mM Tris-HCl, 0.1 M NaCl, 1 mM Benzamidine pH 7.4, Molecular Weight: 58.8 kDa, Purity: greater than or equal to 95%, Storage Temperature: -80 deg C Synonyms: Stuart factor, Stuart-Prower factor, Size: 400 ug