Detection of recombinant protein in mouse plasma. Plasma (0.1 μL) from mice of the indicated prothrombin genotype was analyzed by gel electrophoresis and Western blotting with polyclonal antimouse prothrombin antibodies. Two heterozygous Cf2^+/- mice were injected with 45 μg or 110 μg of aaII 20 minutes before blood sampling. Purified rrII was included in the last lane as a size standard.