Enkephalin, methionine formula

The structures of higher peptides follow in an analogous fashion. Figure 27.7 gives the structural formula and amino acid sequence of a naturally occurring pentapeptide known as leucine enkephalin. Enkephalins are pentapeptide components of endorphins, polypeptides present in the brain that act as the body s own painkillers. A second substance, known as methionine enkephalin, is also present in endorphins. Methionine enkephalin differs from leucine enkephalin only in having methionine instead of leucine as its C-terminal amino acid. 

Two pentapeptides found in the brain are known as enkephalins, namraUy occurring analgesics (pain relievers). For molecules of this size, abbreviations for the amino acids are more convenient than structural formulas. The same notation is used for the amino acid sequence, with the N-terminal amino acid listed first and the G-terminal listed last. The two peptides in question, leucine enkephalin and methionine enkephalin, differ only in their Ckterminal amino acids. 

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See also in sourсe #XX -- [ ]

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