The amino acid composition of chick erythrocyte nucleohistone

• 1.1. Three samples of histone isolated from chick erythrocyte nuclei by a method originally described for the isolation of chromosomes have been analyzed for their content of 18 amino acids by microbiological methods.
• 2.2. Approximately 96% of the total nitrogen of the protein was accounted for by 16 amino acids.
• 3.3. The amino acid content of erythrocyte nucleohistones exhibited some variations when the three preparations of protein from the same tissue were compared.
• 4.4. Tryptophan was not found in any of the hydrolyzates of the erythrocyte nucleohistones.
• 5.5. Small amounts of methionine were consistently recovered in the hydrolyzates from the red cell histones. Cystine was not detected; if present, its content in the protein is less than 0.1%.
• 6.6. The alanine content of the histone samples studied was found to be much higher than that reported by other workers. With the exception of lysine, this amino acid accounted for more of the amino acid residues of the protein than any other.
• 7.7. A higher ratio of lysine to arginine was found in the red cell nucleo-histones contrary to the reports of previous workers who found the opposite to be true.