Isopeptide bond

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N ε -γ- L -glutamy- L -lysine contains an isopeptide bond . In the case of glutamic acid, the linkage takes place via the terminal carboxy group and in the case of lysine via the terminal amino group.

In biochemistry, the special form of an amide bond between the pendant ε- amino group of L- lysine and the pendant carboxy group of L -aspartic acid or L -glutamic acid is referred to as isopeptide bonds . The amino acids are therefore not linked via amino and carboxy groups in the α position. Isopeptide bonds are, for example, closed between lysine and glutamine in the covalent linkage of fibrin in the context of blood clotting by factor XIII.

α-peptide bonds and ω-peptide bonds are not isopeptide bonds

Glutathione (γ- L -glutamyl- L -cysteine ​​glycine) is a tripeptide with a γ-peptide bond (= example of an ω-peptide bond) and an α-peptide bond . Glutathione does not contain any isopeptide bonds as the α-amino group of L- cysteine ​​is involved in the formation of the γ-peptide bond . The α-carboxy group of L- cysteine ​​and the α-amino group of glycine are involved in the α-peptide bond ; this is a common peptide bond and therefore also not an isopeptide bond.

In the case of an α-amino acid which, in addition to the α-amino group, contains a second amino group in the ω-position, e.g. B. L - lysine , and another α-amino acid which is linked to the terminal amino group of the first amino acid via the α-carboxy group, creates an ω-peptide bond. There are also α-amino acids which contain a second carboxy group in addition to the α-carboxy group, e.g. B. L - aspartic acid and L - glutamic acid . If in this case an amide bond is formed via the terminal second carboxy group and the α-amino group of a further α-amino acid, an ω-peptide bond is also formed. Mixed forms also occur in nature, for example the tripeptide glutathione (γ- L -glutamyl- L- cysteine ​​glycine) contains one α-peptide bond and one ω-peptide bond.

Individual evidence

  1. ^ A b Hans-Dieter Jakubke, Hans Jeschkeit: amino acids, peptides, proteins , Verlag Chemie, Weinheim, p. 99, 1982, ISBN 3-527-25892-2 .
  2. ↑ Otto-Albrecht Neumüller (Ed.): Römpps Chemie-Lexikon. Volume 2: Cm-G. 8th revised and expanded edition. Franckh'sche Verlagshandlung, Stuttgart 1981, ISBN 3-440-04512-9 , p. 1511.