Lysinoalanine structure

Alkali-Induced Lysinoalanine Formation in Structurally Different Proteins... 

Lysinoalanine formation in casein, lactalbumin, and wheat gluten was measured at 65°C at various pH s for 3 hours. Factors that control the extent of formation of the unnatural amino acid lysinoalanine during food processing and thus the degree of crosslinking in structurally different proteins are discussed. 

The enthusiasm and effort of able co-workers produced the results discussed here. John L. Morell determined the structure of nisin, H. H. Kiltz and E. Nebelin that of subtilin. H. H. Kiltz initiated the studies on cinnamycin, since then advanced by H. C. Chen and C. H. Chapin. Judith H. Brown is responsible for the information about duramycin. The studies on lysinoalanine are being continued by J. H. Brown, S. Nanno, and C. H. Chapin. 

The mechanism of the observed cellular action of lysinoalanine is not well understood (Finot et al., 1977, Finot, 1983 Engelsma et al., 1979 Reyniers, 1979 Leegwater and Tas, 1980). The possible interaction of LAL with metal ions needs to be explored, however, in view of the recent observations both here and by Hayashi (1982) that LAL inhibits the enzymatic activity of metallo-enzymes such as carboxypeptidase, which contains zinc as part of its active site. The inhibition appears reversible since carboxypeptidase activity was regenerated following the addition of zinc sulfate to the LAL-inactivated enzyme. Inhibition is not surprising since LAL contains three amino and two carboxyl groups and structurally resembles ethylenediaminetetraacetic acid (EDTA), a well-known metal chelator. 

Such treatments, however, can induce chemical changes in the secondary as well as primary structure of the protein. These includes racemization of amino acids and crosslinking that leads to the formation of new amino acids (Masters and Friedman, 1980 Friedman et al., 1981). Lysinoalanine (LAL) is one of these amino acids (Friedman, 1982). These chemical changes are of nutritional concern because alkali-treated protein containing protein-bound LAL can produce renal lesions when fed to rats (Woodard et al., 1975). These cytomegalic alterations are characterized by an enlargment of cells of the pars recta epithelium, with disturbances in mitosis and DNA synthesis. 

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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