Stability of the lyophilized F(ab')2 fragments of horse tetanus antibodies isolated by affinity chromatography.

F(ab')2 fragments of horse tetanus antibodies were obtained from horse hyperimmune sera after peptic digestion. The digest was passed through a column of tetanus toxoid coupled with Sepharose 4B, F(ab')2 fragments were eluted with a solution of 5 mM HCl in 150 mM NaCl and the eluates were concentrated by ultrafiltration and lyophilized. Glycine and human serum albumin were used as stabilizing agents. Polyacrylamide gel electrophoretic mobility and molecular weight of the fragments remained unchanged after lyophilization. Freeze-dried preparations stored two months at 56 degrees C showed only a slight decrease in antitetanus activity. The ORD measurements and spectrophotometric determinations of unfolding over pH range 2.1-5.0 show that the F(ab')2 fragment structure is highly stable in acid medium.