Electron microscopic studies of the sickling phenomenon have described at least three different structural arrangements of sickled hemoglobin, including empty hexagonal crystals, microtubules, and solid rods. It is unlikely that sickling results in several different polymers, and it is essential to determine the true structure of sickled hemoglobin in order to define the mechanism of molecular assembly. The present study has explored the fine structure of gels formed in cell-free solutions of normal and sickle reduced and oxyhemoglobin. Gels of reduced sickled hemoglobin consisted entirely of solid rods. The gels formed from sickle oxyhemoglobin, normal oxyhemoglobin, and normal reduced hemoglobin contained masses of hollow polymers essentially identical in appearance with microtubules. These findings indicate that solid rods are the characteristic polymers of sickled hemoglobin and tubular polymers represent aberrant structures which are not related to erythrocyte sickling.

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