The Val34Leu polymorphism in the A subunit of coagulation factor XIII contributes to the large normal range in activity and demonstrates that the activation peptide plays a role in catalytic activity.

There is a wide normal range of coagulation factor XIII activity that has never been adequately explained. A polymorphism substituting leucine for valine at position 34 in the activation peptide of the A subunit of factor XIII has recently been discovered in nondeficient individuals, and the present studies indicate that the leucine substitution results in a significant increase in transglutaminase activity. The frequency of the Leu34 allele in the Australian Caucasian population is 0.27, which is high enough to suggest that the inheritance of either the Val34 or Leu34 alleles may contribute to the wide normal range of activity. Although there has been structural evidence indicating that the activation peptide does not dissociate from the enzyme after thrombin cleavage, the discovery of elevated activity resulting from the Leu34 substitution is the first direct evidence that the activation peptide plays a continuing role in the function of factor XIII.