Summary
Incubation of a factor Vlll-rich fraction of plasma with a high concentration of salt
confirmed the production of both high (HMW) and low (LMW) molecular weight factor
VIII clotting activity (FVIIIC) as determined by agarose gel filtration but with considerable
overlap. The electrophoretic mobility of factor VIII related protein (FVIIIRP) detected
by precipitating rabbit antiserum was not affected by this treatment and LMW FVIIIC
devoid of FVIIIRP was apparently produced. At low concentration the reducing agent
dithiothreitol (DTT) altered the electrophoretic mobility of FVIIIRP. At higher concentrations
it altered both its mobility and antigenicity and an LMW FVIIIRP was produced. Contrary
to the findings of other workers no LMW FVIIIC devoid of FVIIIRP was produced. In
further studies factor Vlll-rich plasma fraction was treated with sepharose beads
to which had been coupled a non-coagulation inhibitory precipitating rabbit antibody
to FVIIIRP. Both FVIIIRP and FVIIIC were taken up by the beads but after elution with
1.5 M NaCl, FVIIIC of LMW and devoid of FVIIIRP was selectively removed. Antisera
raised to LMW FVIIIC produced with 1.5 M NaCl either by the gel filtration or affinity
chromatography methods inhibited FVIIIC and precipitated with HMW factor Vlll-rich
fractions. The results were consistent with the possibility that factor VIII clotting
activity and FVIIIRP exist in plasma as a non-covalently bound complex.