Regulatory Mechanisms
Serine
protease inhibitors (Serpins):
Examples
include:
Role
heparin plays:
Antithrombin
(AT) –
inactivates thrombin
Required
by both antithrombin and heparin cofactor II
Heparin
cofactor II –
inactivates thrombin
Therapeutic heparin (>17 saccharide units) increases AT activity by 1000 fold
Binds AT and thrombin forming an inactive AT-thrombin complex that is released
from heparin
a1-antitrypsin
–
a2-macroglobulin
Low molecular weight heparin (<17 units) binds AT and thrombin but does not inactivate
thrombin. Does inactivate Xa and other serine proteases
Reversibly inhibits serine proteases