Table 2. Summary of Results Obtained with Factor Va Molecules Truncated at the COOH Terminus of the Heavy Chain in a Clotting Assay and in a Prothrombinase Assay.

	impaired clottinga	increased kcatb
Gerads et al. (18)	+	+ (17%)c
Bakker et al. (19)	+d	+ (12%)e
Camire et al. (20)	+	+ (18%)
Kalafatis et al. (21)	+	+ (19%)f
Toso and Camire (37)	+	+ (29−50%)g

^aThe plus sign indicates that the molecules missing part or the entire COOH-terminal portion of the heavy chain are impaired in clotting activity.

^bThe plus sign indicates that the factor Va molecules missing part or the entire COOH-terminal portion of the heavy chain have increased catalytic efficiency when they are assembled in prothrombinase. In parentheses are the percent increases in k_cat compared to that of prothrombinase assembled with plasma-derived factor Va or to that of wild-type recombinant factor Va reported in each study.

^cAll results reported were obtained with proteins of bovine origin.

^dFrom ref (18); the authors also report results obtained with human factor Va and clotting assays with factor V-deficient plasma.

^eAll work was performed with proteins of human origin and is complementary to the work reported in ref (18).

^fThe k_cat of factor Va_IIa/NN in the assay using purified reagents and a chromogenic substrate to assess for α-thrombin formation is reported here (Table 1).

^gAll results were obtained with recombinant proteins. The factor V construct used for expression was missing a major portion of the B domain of the molecule.