Thromb Haemost 1988; 59(03): 372-377
DOI: 10.1055/s-0038-1647498
Original Article
Schattauer GmbH Stuttgart

Thrombin-Independent Activation of Platelet Factor XIII by Endogenous Platelet Acid Protease

Garry W Lynch
The Monash University Department of Medicine, Alfred Hospital, Prahran, Victoria Australia
,
Sharron L Pfueller
The Monash University Department of Medicine, Alfred Hospital, Prahran, Victoria Australia
› Author Affiliations
Further Information

Publication History

Received 07 April 1987

Accepted after revision 11 January 1988

Publication Date:
29 June 2018 (online)

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Summary

Platelets contain factor XIII, an A subunit zymogen form of transglutaminase (TGase), that is activated by thrombin. In addition a thrombin-independent TGase (A#) was observed. A# was formed in platelet preparations lysed at acid pH, and its generation inhibited by protease inhibitors and alkaline pH. When maximal A# activity was generated in acidified lysates no further TGase activity could be induced by subsequent treatment with thrombin. Both FXIII zymogen and A# copurified as for F XIII, from either alkaline or from acidified platelet lysates respectively, by the conventional procedure. The pH optima, Km’s for NN dimethyl casein, molecular weights, heat lability of active forms, requirements for calcium and reducing agents, and immunological characteristics of both TGases were the same. Studies with inhibitor substrates suggested that a thrombin-like cathepsin C or carboxypeptidase was responsible for A# formation. Purified F XIII zymogen could be activated directly by cathepsin C. Thus, the predominant, and probably only, TGase of platelets is factor XIII, which may be activated either by thrombin or by endogenous platelet acid protease(s).