Summary
Allegedly factor V 1-stage bioassays and an established mode of 2-stage thrombingeneration
tests are performed with three alternative prime activators : (A) thrombokinase; (B)
Russell’s viper venom (Stypven); (C) tissue thromboplastin (Simplastin), each with
adequate cofactors. Study of effects of thrombin and factor V mixtures or preincubates
shows a marked apparent potentiation in the 1-stage tests, but no real evidence of
such in the 2-stage methods, although these are equally sensitive to changes in factor
V activity. Cited (13) new observations in the 1-stage experiments record: (a) that
no preincubation of thrombin and factor V is necessary; (b) that thrombin-treated
factor V (= Vt) potentiates anew with a second thrombin addition ; and (c) that Vt
+ thrombin again shows a shift in the Sephadex G-200 elution pattern similar to the
difference between the original V and Vt. These facts all constitute a convincing
refutation of the theory that factor V is activated by thrombin to a postulated ‘Va’.
What is obviously needed is a complete reinterpretation of the uniquely 1-stage results.
A novel approach is based on testings of selective combinations of the 5 basic components
(prothrombin, thrombokinase, Ca++, phospholipid, and factor V) required for thrombin generation by <1 ìg/ml thrombokinase.
The results permit the conclusion that the true explanation is to be found in activities
of the prime activator, especially thrombokinase, as controlled by availabilities
of the 3 cofactors, namely, factor V, Ca++ions, and phospholipid. Factor V was previously shown to be a determinant of thrombokinase
activity during thrombin generation. In no way should the evidence be misinterpreted
as any V → Va activation. A new enzymic and colloidal clotting mechanism (12) is reaffirmed,
in which factor V has a dual role.
