Conformational Changes and Loss of Opsonic Function in Frozen or Heat-Treated Plasma Fibronectin

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Abstract
Using human peripheral blood monocytes to assay opsonic protein activity, the efficiency of various procedures for isolating fibronectin from plasma for experimental or therapeutic use was examined. The protein''s opsonic activity after cold storage and after heat treatment to inactivate hepatitis virus was assessed. The purification procedures recovered only 30% of available plasma fibronectin while cold storage and heat treatment of the purified protein removed all of its remaining opsonic activity. This was associated with no alteration in overall MW or in subunit size but was accompanied by changes in UV spectrum, suggesting a conformational change in the protein structure. Initial experiments to protect the purified protein against these changes were unsuccessful and unless further attempts are more encouraging, fresh-frozen plasma may be the only current economic source of opsonically active fibronectin. Since this would waste other valuable proteins required for other purposes, the widespread use of plasma fibronectin outside of clinical trials may be unjustified at this present time.