F

Following cleavage, the two chains are linked via a divalent metal ion bridge. Factor V binds to phospholipid surfaces via binding sites in the light chain. Inactivation of factor V occurs via activated

protein C

and its cofactor

protein S

by cleavage at Arg506. Although it is predominantly synthesized in the liver (plasma factor V),

megakaryocytes

also synthesize factor V, which is stored in platelet a-granules (platelet factor V). Platelet

factor V is secreted upon platelet activation and accounts for approximately 20% of the body mass of factor V. Factor V has a binding-protein multimerin that acts in a similar manner to

Von Willebrand Factor

and factor VIII. Plasma concentration of factor V is 0.5 to 1.0 mg/dl (0.5 to 2.0 U/ml). It has a half-life

of approximately 12 h. Values for premature and full-term infants during the first 6 months of life are given in

Reference Range Tables XIII

and

XIV

.