The interaction of fragment 1 of prothrombin with the membrane surface is a prerequisite for optimum expression of factor Va cofactor activity within prothrombinase Academic Article uri icon

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abstract

  • SummaryIncorporation of factor (F) Va into prothrombinase directs prothrombin activation by FXa through the meizothrombin pathway, characterized by initial cleavage at Arg320 We have shown that a pentapeptide with the sequence DYDYQ specifically inhibits this pathway. It has been also established that Hir54–65(SO3 -) is a specific inhibitor of prothrombinase.To understand the role of FVa within prothrombinase at the molecular level, we have studied thrombin formation by prothrombinase in the presence of various prothrombin-derived fragments alone or in combination. Activation of prethrombin 1 is slow with cleavages at Arg320 and Arg271 occurring with similar rates. Addition of purified fragment 1 to prethrombin 1 accelerates both the rate of cleavage at Arg320 and thrombin formation.Both reactions were inhibited by Hir54–65(SO3 -) while DYDYQ had no significant inhibitory effect on prethrombin 1 cleavage in the absence or presence of fragment 1. Similarly, activation of prethrombin 2 by prothrombinase,is inhibited by Hir54–65(SO3 -), but is not affected by DYDYQ.Addition of purified fragment 1•2 to prethrombin 2 accelerates the rate of cleavage at Arg320 by prothrombinase. This addition also results in a significant inhibition of thrombin formation by DYDYQ and is concurrent with the elimination of the inhibitory effect of Hir54–65(SO3 -) on the same reaction. Finally, a membrane-bound ternary complex composed of prethrombin 2/fragment 1•2/Hir54–65(SO3 -) is inhibited by DYDYQ. Altogether,the data demonstrate that membrane- bound fragment 1 is required to promote optimum FVa cofactor activity which in turn is translated by efficient initial cleavage of prothrombin by prothrombinase at Arg320.

authors

  • Bukys, Michael
  • Orban, Tivadar
  • Kim, Paul
  • Nesheim, Michael
  • Kalafatis, Michael

publication date

  • 2008

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