Freeze-drying of oxyhemoglobin: protection against oxidation in the presence of EDTA salts, sulfonic acid buffers, and pantothenic acid derivatives.

Hemoglobin was freeze-dried in the presence of salts of EDTA, sulfonic acids used as buffers, or derivatives of pantothenic acid. At 0.25 M most of the compounds effectively inhibited the formation of methemoglobin. The various model compounds used (sodium zinc EDTA, tris(hydroxymethyl) methylaminopropanesulfonic acid, and DL-pantothenol) produced similar decreases in methemoglobin formation as a function of the concentration of protective agent between 0.01 and 0.20 M. Experiments on the storage of the freeze-dried materials revealed substantial denaturation of oxyhemoglobin after 12 months at 4 degrees C. On the whole, these compounds were less effective than amino acid salts, during both desiccation and storage. The multiplicity of compounds that inhibit the denaturation of hemoglobin during freeze-drying indicates that their mode of action is nonspecific.