activator
[ak´tĭ-va″ter] a substance that makes another substance active or reactive, induces a chemical reaction, or combines with an enzyme to increase its catalytic activity.
tissue plasminogen activator (TPA, t-PA) (
t-plasminogen activator) a serine endopeptidase synthesized by endothelial cells, the major physiologic activator of
plasminogen; when bound to
fibrin clots it catalyzes the conversion of plasminogen to
plasmin by hydrolysis of a specific arginine-valine bond. It can be produced by recombinant technology for use in
thrombolytic therapy. It acts directly on blood clots and therefore presents a small risk of systemic bleeding; occasionally allergic reactions may occur.
u-plasminogen activator (
urinary plasminogen activator) a serine endopeptidase that acts as a plasminogen activator by catalyzing the preferential cleavage of plasminogen at the same arginine-valine bond where
t-plasminogen activator cleaves. It is produced in the kidney and excreted in the urine and is used in
thrombolytic therapy (when used as a pharmaceutical, it is usually called
urokinase). Unlike t-plasminogen activator or prourokinase, it does not require
fibrin for activity. Called also
urokinase.
Miller-Keane Encyclopedia and Dictionary of Medicine, Nursing, and Allied Health, Seventh Edition. © 2003 by Saunders, an imprint of Elsevier, Inc. All rights reserved.