Dehydroalanine lysinoalanine precursors

The inspection of cinnamycin (4) and duramycin (5)—prompted by their content in lanthionine and /3-methyllanthionine—for the presence of ,/3-unsaturated amino acids was negative. However, cinnamycin as well as duramycin contain lysinoalanine, among other amino acids rarely seen in nature. Did the peptides at one time contain dehydroalanine and did it serve as a precursor for lysinoalanine If the answer to this question were yes, which amino acids, in turn, are potential precursors of dehydroalanine ... 

The ,/ -unsaturated amino acid dehydroalanine is a necessary precursor for the formation of lysinoalanine. The chemical events covered in the preceding discussion took place in the in vitro environment. Do a S-unsaturated amino acids play a role in any in vivo environment other than that of microorganisms From the latter domain have been isolated the peptides richest in ,/ -unsaturated amino acids, nisin (I) and subtilin (10). No direct evidence is available at this time to document convincingly the possible physiological role of ,/ -unsaturated amino acids in higher organisms. That dehydroalanine is the constituent amino acid of a plant protein has been reported for phenylalanine ammonia lyase from potato tubers (22). There is one case on record for the presence of... 

As already mentioned, dehydroalanine is the postulated reactive precursor for lysinoalanine. Direct evidence for dehydroalanine reactivity was obtained by Friedman et al. (1977). They showed that dehydroalanine derivatives convert lysine side chains in casein, bovine serum albumin, lysozyme, wool, or polylysine to lysinoalanine residues at pH 9 to 10. Related studies showed that protein SH groups generated by reduction of disulfide bonds are completely alkylated at pH 7.6 to lanthionine side chains. These studies demonstrate that lysinoalanine and lanthionine residues can be introduced into a protein under relatively mild conditions, without strong alkaline treatment. They also imply that it should be possible to explore nutritional and toxicological consequences of lysinoalanine and lanthionine consumption in the absence of racemiza-tion (see below). 

As reported by Friedman (1982), the major factor controlling the production of lysinoalanine, once the dehydroalanine precursors are formed, could be the location and availability of "partners for crosslink formation. When they are adjacent or close by, lysinoalanine formation could be facilitated. When treatment allows it, more lysinoalanine could be formed, even involving cross-chain links. Thus, the capacity for forming LAL would vary not only with the treatment applied but with the nature of the protein, involving its secondary or tertiary structure as well as its primary one. 

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