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Studies of Transfer Ribonucleic Acids and of Hemoglobin Synthesis in Sheep Reticulocytes

From the ¹ From the Department of Biochemistry and the Division of Medical Genetics, University of Oregon Medical School, Portland, Oregon 97201

We have analyzed the methionine and isoleucine acceptor capacity of transfer ribonucleic acid purified from reticulocytes of sheep carrying different globin genes and synthesizing characteristically different hemoglobins. It had been previously established that hemoglobin A (₂ß₂^a) is synthesized by A/A homozygotes in the early stages of anemia, whereas these same sheep switch over to hemoglobin C (₂ß₂^c) synthesis when they are severely anemic. On the other hand, only hemoglobin B (₂ß₂^b) is synthesized by normal or by heavily anemic B/B homozygotes. It is also known that hemoglobin A contains 0 isoleucine and 6 methionine residues, hemoglobin B contains 0 isoleucine and 8 methionine residues, and hemoglobin C contains 2 isoleucine and 2 methionine residues.

We found that the isoleucine acceptor capacity is 2 to 3 times higher in transfer ribonucleic acid from reticulocytes synthesizing hemoglobin C as compared with cells synthesizing hemoglobins A or B. However, the isoleucine transfer ribonucleic acids from these reticulocytes could not be distinguished in their chromatographic behavior. Methionine-specific transfer ribonucleic acid is resolved by chromatography into two peaks. The smaller of these peaks is relatively decreased in quantity in reticulocytes synthesizing hemoglobin C. We conclude that the relative quantities of the different transfer ribonucleic acids are correlated with the amino acid composition of the sheep hemoglobins being synthesized. Furthermore, the changes are specific for the different isoaccepting species of transfer ribonucleic acid.

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