An immunochemical method for the quantitative determination of specific soluble proteins in individual erythrocytes has been described. Application of the method revealed:

1. From 0.5 to 0.9 per cent of the normal adult erythrocytes studied contained small amounts of γ-chains, from 2.5 to 12.5 µµg. as hemoglobin per cell.

2. In cord blood of normal infants of 38 weeks’ gestation, significant numbers of erythrocytes were found which contained either γ-chains or β-chains or both, independently of carbonic anhydrase B.

3. Once initiated within a given erythrocyte, β-chain synthesis in that cell rapidly approached adult rates. Derepression of carbonic anhydrase B synthesis was independent of derepression of hemoglobin synthesis, and in fetal cells which contained carbonic anhydrase B the amount found was well below that of most adult erythrocytes.

4. In 4 patients homozygous for hemoglobin S and in 2 persons heterozygous for thalassemia, an increase in F hemoglobin was associated with an increase in γ-chain content of individual erythrocytes as well as an increase in the number of erythrocytes containing γ-chains; in 2 patients homozygous for thalassemia, an unusual distribution of cells with increased γ-chain content was observed.

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