Western blot analysis of plasma and platelet FV and platelet fibrinogen. (A) Samples prepared from pooled C57BL/6 mice are shown as follows, with concentrations reported as a percentage relative to undiluted plasma: (i) 20% solution of platelet-rich plasma; (ii) 20% platelet-poor plasma (PPP); (iii) 10% PPP; (iv) 100% platelets, centrifuged from PRP; (v) 100% platelets, gel-filtered. Single-chain FV (∼300 kDa) is seen near the top of the gel. Fainter bands below represent nonspecific signals that are also present on Western blots of plasma from mice genetically deficient for FV (not shown). (B) Western blots of the peak platelet fraction prepared from an unirradiated normal C57BL/6 mouse (control), an Fv–wild-type FLC (Fv^+/+), and an Fv-null FLC (Fv^–/–) recipient are shown. For each panel, equal volumes of the total platelet peak fraction, supernatant component (Sup.), and pellet/platelet component (Plt.) were separated on an SDS polyacrylamide gel (see “Materials and methods”).