Chromogenix S-2222™ is a chromogenic substrate for Factor Xa. It is also very sensitive to trypsin. The substrate has been used for the determination of:

  • Factor X in plasma
  • Factor Xa in plasma
  • Factor Xa inhibitor in plasma
  • Heparin in plasma
  • Factor VIII in plasma
  • Coagulating enzyme from horseshoe crab plasma
  • Trypsin in duodenal fluid

The substrate is also sensitive to subtilisin, acrosin and Factor XIIa but insensitive to most other enzymes tested, e.g. Factor IXa, kallikrein (glandular and plasma) and papain-like enzymes.

Each vial contains chromogenic substrate S-2222™ 25 mg and mannitol 120 mg as a bulking agent.

Molecular wt: 741.3

Formula: Bz-Ile-Glu(g-OR)-Gly-Arg-pNA·HCl R=H (50%) and R=CH3 (50%)

Chemical name: N-Benzoyl-L-isoleucyl-L-glutamyl-glycyl-Larginine-p-nitroaniline hydrochloride and its methyl ester

chromogenix chromogenic substrate assay test kit

Factor Xa, which has a molecular weight of 44 KDa, is the activated form of Factor X (MW: 59 KDa).

The International Units of Factor X correspond to the amount of Factor X contained in 1 ml of normal plasma. This is about 8 mg/l or 0.13 µmol/l.

Since there is no WHO standard for FXa, one would assume that if all the Factor X in normal plasma was converted to the activated form, the Factor Xa concentration would be approximately 5.7 mg/l.

The activity of human Factor Xa as calculated from the kinetic tables is 1.5 nkat/µg with the chromogenic substrate S-2222™, and 4.4 µkat/µg with the chromogenic substrate S-2765™.

The activity of 1 µg of Factor Xa as determined by Frieberger (1) is 1.9 nkat chromogenic substrate S-2222™.

Thus, 1 plasma equivalent unit of Factor X would correspond to 15.2 nkat chromogenic substrate S-2222™.

Friberger P et al.
Synthetic peptide substrate assays and fibrinolysis and their application on automates. In: Seminars in Thrombosis and Haemostasis, Vol. 9, 281-300 (1983).