Histidine copolymer with aspartic acid

Fig. 2. Ultraviolet absorption spectra of a copolymer of aspartic acid and histidine before and after heating or after treating with alkali. The spectrum of the alkali-treated sample was not significantly affected by heating. Taken from Rohlfing and Fox (16).

Earlier studies include those of Merrifield and Wooley (i27) and of Katchalski et al. (128). They prepared poly-L-histidine and its copolymers with other amino acids and showed them to be active in the hydrolysis of PNPA. Noguchi and Saito prepared poly-L-histidine, its copolymers with other amino acid residue (glutamic acid 2, aspartic acid 3, serine 4, alanine 5, cystein 6, lysine 7, e-aminocaproic acid S, and tyrosine 9), and various dipeptides containing the histidyl residue 1), (129,130). The... 

Pinna nobilis tropomyosin contains no proline (Bailey, 1957), which is consistent with a helical molecule. As might be expected from the study of a 5% copolymer of L-tyrosine with L-glutamic acid (see Section III, F), the presence of small amounts of tyrosine and histidine in this protein has no appreciable rotatory effect. This protein contains relatively large amounts of amino acids that do form standard helical polypeptides—glutamic acid, 21 % lysine, 8% alanine, 12% and leucine, 12.5 %—but it also has 4 % valine, 6 % serine, and 13 % aspartic acid. If these residues behaved as they and their analogues appear to do in synthetic polypeptides, either pre-... 

When proteinoids were heated in buffer at pH 6.2 or 6.8, loss of catalytic activity was observed. The extent of loss ranged from 95 to 11% (Table II). Those proteinoids that initially showed higher levels of activity relative to histidine were the most affected by the heat treatment. After heating, the level of activity was comparable to that of the equivalent amount of histidine, or to that of mineral acid hydrolysates of the polymer. Under similar conditions, a-chymotrypsin was 97% inactivated. The fact that the control tests on L-histidine or A -carbo-benzoxy-L-histidine showed no effect is consistent with the inference that inactivation is due to disruption of a macromolecular conformation. Copolymers prepared from only aspartic acid and histidine were also active on NPA and were inactivated by the heat treatment. The percentages of inactivation ranged from 62 to 19. Polymers prepared and processed under aseptic conditions were both catalytically active and subject to inactivation by heat. These experiments were performed as routine verification that the respective phenomena do not result from the presence, and subsequent denaturation, of contaminating microbial enzymes. 

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