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The Purification of Formol Diphtheria Toxoid by Multi-Membrane Electro-Decantation

From the Virus Research Unit, Department of Pathology and the Department of Chemistry, University of Cape Town, South Africa

Abstract

Formol diphtheria toxoid was purified by a combination of multi-membrane electro-decantation, ammonium sulphate fractionation and acid precipitation, yielding a product with a potency of 2950 L_f/mg protein nitrogen without impairing the antigenieity in guinea-pigs.

Physieochemical investigation showed that the purified toxoid was homogeneous by gel diffusion, electrophoresis, diffusion and sedimentation measurements. Using sedimentation and diffusion data a molecular weight of 73,300 and a frictional ratio of 1.34 were calculated.

The iso-electric point of formol diphtheria toxoid, as determined by a new method using a modified form of M.M.E.D. apparatus, was found to be pH 4.15 and pH 4.25 in acetate buffers of ionic strengths 0.05 and 0.025 respectively.

Footnotes

¹ Present Address: Seravac Laboratories, Hawkins Avenue, Epping Industrial Area, Cape Town, South Africa.