This document discusses chromogenic substrates, which are peptides linked to a chromophore that are used to detect and measure the activity of proteolytic enzymes like thrombin and factor Xa. Chromogenic substrates are cleaved by these enzymes, releasing the chromophore p-nitroaniline which turns yellow and can be quantified. The document provides examples of specific chromogenic substrates for various enzymes and describes their use in clinical assays to measure coagulation factors, antithrombin, heparin, and activated protein C.

1. CHROMOGENIC SUBSTRATE TECHNOLOGY Giovanni Russi

3. Chemical structure Prothrombin, the natural substrate of FXa, is cleaved by FXa at two positions, each proceeded by the same four amino acid sequence. FXa activity can be determined by the chromogenic substrate S-2222 which is composed of the same amino acids coupled to a chromophore

4. Chemical structure Blocking group Chromophore Residues

7. Classes of proteases *Asp not always present

11. The proteolytic reaction Formation of an acyl-enzyme intermediate

12. The proteolytic reaction Hydrolysis of the acyl-enzyme intermediate

13. Enzyme kinetics E + S ES E + P K1 K3 K2 V = Vmax [S] [S] + K m K m = k 1 k 2 + k 3

18. Application of the chromogenic technology: Antithrombin Heparin Protein C

19. Antithrombin Antithrombin is the major thrombin inhibitor, accounting for approximately 80% of the thrombin inhibitory activity in plasma.

23. Thrombin inhibition catalysed by heparin AT R H AT H IIa AT H IIa IIa AT H IIa R P P P P R R

24. FXa inhibition catalysed by heparin AT R H AT H Xa AT H Xa Xa AT H Xa R P P P P R R

25. Antithrombin monitoring

26. Antithrombin monitoring chromogenic activity assays Chromogenic heparin cofactor activity assays: - The sample is incubated with heparin and an excess amount of thrombin or FXa. The residual thrombin or FXa then cleaves a chromogenic substrate AT + Heparin [AT*Heparin] [AT*Heparin] + FXa (excess) [AT-FXa- Heparin] + FXa(residual) Chromogenic substrate FXa(residual) Peptide + pNA

27. Antithrombin: anti-FXa assay Sample/Standard dilution: 25  l sample+ 3000  l saline Procedure Volumes Diluted sample/standard 50  l Factor Xa (2.9 nkat/ml in Hep Buffer) 50  l Incubate at 37°C 90 sec S-2765 (0.8 mg/ml) 50  l Read  A/min at 405 nm for rate method or add 50  l Acetic acid after 90 sec incubation for end-point method.

28. Antithrombin: anti-FXa assay

30. Heparin +

34. Heparin measurements

36. Protein C in the coagulation system Extrinsic pathway Intrinsic pathway TF FVIIa FIXa FVIIIa PL, Ca2+ FXa FX FVa PL, Ca2+ Prothrombin Thrombin Fibrinogen Fibrin Protein C APC Thrombo-modulin Protein S FV

37. Protein C - an anticoagulant Vitamin K dependent proteins: Anticoagulants: protein C and protein S Procoagulants: Factor II, VII, IX and X Synthesised in the liver Glu Gla (glutamic acid residues are converted to gamma-carboxyglutamic acid) The Gla domain binds calcium ions which form a bridge to the phospholipid surfaces on platelets and endothelial cells.

38. Protein C-the structure

39. Protein C- the function Protein C inhibits coagulation through inactivation of FVIIIa and FVa Protein C potentiates the fibrinolytic system by inhibiting PAI-1, the major inhibitor of fibrinolysis.

40. Protein C activation Protein C is activated (to APC) by thrombin. A small peptide is removed. Activation by thrombin alone is slow. The complex thrombin-thrombomodulin activates protein C 20 000 times faster. PC APC TM

44. Coamatic Protein C - the principle Protein C APC Protac S-2366 Peptide + pNA APC

45. Back to the chromogenic substrates……….

46. S-2222 TM  Factor Xa S-2238 TM  Thrombin S-2251 TM  Plasmin and Streptokinase-activated Plasminogen S-2266 TM  Glandular Kallikrein and Factor XIa S-2288 TM  t-PA; other proteases S-2302 TM  plasma kallikrein; Factor XIa; Factor XIIa S-2314 TM  C1s S-2366 TM  activated protein C; factor XIa S-2390 TM  Plasmin S-2403 TM  Plasmin and Streptokinase-activated Plasminogen S-2423 TM  Endotoxin determination S-2444 TM  Urokinase S-2484 TM  Granulocyte elastase S-2586 TM  Chymotrypsin S-2765 TM  Factor Xa S-2772 TM  Factor Xa Product range:

48. Substrate selectivity The Chromogenix catalogue includes a section which shows the cross-reactivity of the substrates with the different enzymes tested

49. Kinetic data The Chromogenix catalogue includes a section which shows the kinetic data of the substrates toward the different enzymes tested

51. The 25 mg Substrates