Glycine residues and

Figure 8.1 Cross section of a tropocollagen molecule showing the internal position of glycine residues and the external location of X and Y molecules. Proline is shown in position Y. (Reproduced by permission from Walton AG. Polypeptide and Protein Structure. New York Elsevier, 1981, p. 309.)...

The protein collagen, from skin and tendons, is composed of approximately 30 percent proline and hydroxyproline and 30 percent glycine. This protein has an unusual structure in which three chains, each with a conformation very similar to that of polyproline, are twisted about each other to make a triple helix. The three strands are hydrogen bonded to each other, through hydrogen bonds between the —NH of glycine residues and the — C=0 groups of the other amino acids. 

Figure 24.30. Glutathione. This tripeptide consists of a cysteine residue flanked by a glycine residue and a glutamate residue that is linked to cysteine by an isopeptide bond between glutamate s side-chain carboxylate group and cysteine s amino group.

The amino-terminal end of the prion protein is rich in histidine and glycine residues, and is believed to be the metal-binding site of the protein. Specifically, the mammalian prion protein... 

These all contain the glycine residue as well as the alanine residue in their molecule in order to eliminate the glycine residue and obtain compounds without the glycine radical, Curtius and van der Linden prepared the following compound —... 

These compounds already exhibit the extraordinary possibilities of synthesis by this method. By continuing the process of preparing the acid chloride of a new polypeptide and again combining it with a polypeptide ester, the synthesis of the complex octadecapeptide, composed of fifteen glycine residues and three leucine residues, was effected in 1907. Its preparation is the best illustration of how this method lends itself to the synthesis of the polypeptides. 

How many tripeptide isomers that contain one glycine residue and two alanine residues are possible ... 

Tussah silk, contains only 27 percent glycine residues, and the pleated sheets are separated by the same distance, 530 pm, rather than alternating as in Bonibyx niori silk. 

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