Histidine separation from other amino acids

Considerable progress in the separation of individual amino acid acceptor RNA s from each other has been reported by Holley and Doctor (80) who have developed a countercurrent system capable of separating valine-, threonine-, histidine-, leucine-, and tyrosine-acceptor RNA s from each other. Tyro e-acceptor RNA isolated after this procedure had a specific activity six times that of the original RNA (6-8 m/tmoles per milligram RNA see also Table VI). 

Figure 39-14. Zinc fingers are a series of repeated domains (two to nine) in which each is centered on a tetrahedral coordination with zinc. In the case of TFIIIA, the coordination is provided by a pair of cysteine residues (C) separated by 12-13 amino acids from a pair of histidine (H) residues. In other zinc finger proteins, the second pair also consists of C residues. Zinc fingers bind in the major groove, with adjacent fingers making contact with 5 bp along the same face of the helix.

Amino acids > as well as ammonia, ) and probably also other primary amines can be determined from the decrease in the wave for phthalaldehyde. In the presence of an excess of phthalalde-hyde a nonreducible compound is formed after the addition of amino compounds. Condensation occurs in most instances in a ratio 1 phthalaldehyde 1 amino acid histidine, lysine and ammonia react in the ratio 3 2. The time necessary for completion of the reaction is between 0 3 hr. (for lysine) and 2-3 hr (for glycine, alanine and ammonia). Because the decrease of the phthalaldehyde wave changes according to the amino acid used, it is necessary in a mixture to separate first the individual amino acids and to use a separate calibration curve for each amino acid. A reaction involving the amino groups of gelatin has also been observed. 

The optical isomers of DL-histidine have been separated by the fractional crystallization (spontaneous resolution) procedure described by Duschinsky (227) but no other applications of this method have been reported. nt-Amino acids are commonly resolved by fractional crystallization from water, ethanol or methanol of the salts formed from the DL-amino acid or a derivative and an optically active form of an organic acid or base. The more insoluble salt is removed and hydrolyzerl, and the optically active amino acid (A) is purified by recrystallizing it from... 

Results of the separation of the activation peptides, obtained as described above, are shown in Figure 3. Amino acid analysis of the peaks showed that the pepstatin was recovered in peak 1 and that peak 4 contained mainly peptide 1-16 (Table I). In addition to the amino acids listed, there were small amounts of histidine, glycine, and alanine. From the quantities of these amino acids and the known sequence of the total activation fragments (5,21,22), it was ascertained that the product was about 90% pure, the slightly high values for several amino acids being caused by contaimination with at least three other peptides. No further purification was considered considered necessary. 

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