Thromb Haemost 1988; 60(02): 298-304
DOI: 10.1055/s-0038-1647048
Original Article
Schattauer GmbH Stuttgart

The Anticoagulant Properties of a Modified Form of Protein S

C A Mitchell
The Department of Medicine, Monash Medical School, Prahran Victoria, Australia
,
S M Kelemen
The Department of Medicine, Monash Medical School, Prahran Victoria, Australia
,
H H Salem
The Department of Medicine, Monash Medical School, Prahran Victoria, Australia
› Author Affiliations
Further Information

Publication History

Received 19 November 1987

Accepted after revision 27 June 1988

Publication Date:
28 June 2018 (online)

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Summary

Protein S (PS) is a vitamin K-dependent anticoagulant that acts as a cofactor to activated protein C (APC). To date PS has not been shown to possess anticoagulant activity in the absence of APC.

In this study, we have developed monoclonal antibody to protein S and used to purify the protein to homogeneity from plasma. Affinity purified protein S (PSM), although identical to the conventionally purified protein as judged by SDS-PAGE, had significant anticoagulant activity in the absence of APC when measured in a factor Xa recalcification time. Using SDS-PAGE we have demonstrated that prothrombin cleavage by factor X awas inhibited in the presence of PSM. Kinetic analysis of the reaction revealed that PSM competitively inhibited factor X amediated cleavage of prothrombin. PS preincubated with the monoclonal antibody, acquired similar anticoagulant properties. These results suggest that the interaction of the monoclonal antibody with PS results in an alteration in the protein exposing sites that mediate the observed anticoagulant effect. Support that the protein was altered was derived from the observation that PSM was eight fold more sensitive to cleavage by thrombin and human neutrophil elastase than conventionally purified protein S.

These observations suggest that PS can be modified in vitro to a protein with APC-independent anticoagulant activity and raise the possibility that a similar alteration could occur in vivo through the binding protein S to a cellular or plasma protein.