Dipeptide
A dipeptide is a sometimes ambiguous designation of two classes of organic compounds: Its molecules contain either two amino acids joined by a single peptide bond or one amino acid with two peptide bonds.
In this usage, X dipeptide (with X designating an amino acid) must be understood as di-X peptide. This nomenclature is continued by tripeptide (three amino acids, two peptide bonds), tetrapeptide, and so on; longer chains are called oligopeptide, polypeptide, protein.
Dipeptides are produced from polypeptides by the action of the hydrolase enzyme dipeptidyl peptidase. Dietary proteins are digested to dipeptides and amino acids, and the dipeptides are absorbed more rapidly than the amino acids, because their uptake involves a separate mechanism. Dipeptides activate G-cells found in the stomach to secrete gastrin.
The Bergmann azlactone peptide synthesis is a classic organic synthesis for the preparation of dipeptides.
In this usage, X dipeptide is taken literally: One amino acid X is equipped with two minimal peptide bonds: The C terminus COOH becomes COCH3, the N terminus NH2 becomes NHCH3. For instance, alanine dipeptide is CH3CONHCH(CH3)CONHCH3.
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