The contact-system dependent plasminogen activator from human plasma: identification and characterization

Area of Science:

• Biochemistry
• Hematology
• Molecular Biology

Background:

• Human plasma contains tissue-type plasminogen activator (t-PA) and urokinase-type plasminogen activator (u-PA).
• A third, distinct plasminogen activator (PA) activity has been observed in plasma, initiated by contact system triggers.

Purpose of the Study:

• To identify and characterize the third PA present in human plasma.
• To elucidate the properties and activation mechanism of this contact-system dependent PA.

Main Methods:

• Analysis of dextran sulphate euglobulin fractions of human plasma.
• Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) to determine molecular weight.
• Gel chromatography and isoelectric focusing (IEF) to analyze native form and charge.
• Immunoassays using antibodies against t-PA and u-PA.

Main Results:

• A novel 110 kDa single-chain polypeptide was identified as the smallest unit of the third PA.
• Activation of the contact system converts the inactive polypeptide to an active, cleaved form.
• The native form appears as an oligomer (Mr 600,000) with an isoelectric point (pI) of 4.8.
• The active 110 kDa polypeptide contains cryptic u-PA related antigenic determinants, detectable after SDS denaturation.

Conclusions:

• A third, contact-system dependent PA has been identified in human plasma.
• This PA is a distinct entity, not an intrinsic contact system component or simply t-PA or u-PA.
• Its activation pathway and unique properties warrant further investigation in hemostasis and thrombosis.