Enzymes lysinoalanine

Another common posttranslational modification found in mature lantibiotics is a C-terminal AviCys (Fig. la). This residue is formed by EpiD in epidermin (18). Currently, not much is known about the enzymes that catalyze formation of other unique lantibiotic residues. The cinnamycin gene cluster was cloned recently (19), which set the stage for studies to determine which gene products are responsible for lysinoalanine and fi-hydroxy aspartate formation. 

HP he addition of the e-amino group of lysine across the double bond of dehydroalanine leads to a product known as lysinoalanine (Figure 1). The formation of this amino acid was initially observed in bovine pancreatic ribonuclease when the enzyme was subjected to alkaline conditions. More recently, lysinoalanine has been detected in food products... 

The formation of lysinoalanine in home-cooked food has been reported recently for conditions of preparation well outside the alkaline pH range (18). Is lysinoalanine ubiquitous in the heat- and alkali-treated preparations of man s daily dietary intake, and has it been so for ages If the answer to this question is yes, man must have developed (induced ), since the days of having learned to tame the fire, enzymes or enzyme systems for the effective metabolic utilization of lysinoalanine. The early application of peptides with radiolabeled lysinoalanine becomes a more urgent one. 

The nephrotoxic amino acid, lysinoalanine [18810-04-3] formed upon alkaline treatment of protein, was reported in 1964 (108). Its toxicity seems to be mitigated in protein in that it is not released by normal digestion (109). Naturally occurring new amino acids, which can be classified as proteinaceous or non-proteinaceous, can, as in the case of those from some legumes, show a remarkable toxicity (110). For the details of amino acid toxicity, see reference 6. Enzyme inhibition by amino acids and their derivatives have been reviewed (111). 

Heat or alkaline treatment of foods, feeds or pure proteins can result in desirable changes in the food system but treatments can also lead to the formation of a series of xenobiotics, one of which is lysinoalanine. Alkaline treatment of proteins can be intended to improve flavor or texture (1-3), to destroy toxins or enzyme inhibitors and to promote solubilization of the protein for the purpose of isolation (4, 5). Heat treatment can be used for sterilization or to alter the physical characteristics of the protein or constituents of the food system. 

Although proteolytic deamidation at alkaline pH was shown to be useful for increasing the surface properties of some proteins, as described earlier, proteolysis is not inevitable for other types of proteins. Furthermore, the alkaline pH condition damaged amino acid residues of protein, for instance, race-mization or the formation of lysinoalanine. Therefore, it is more desirable to use enzymes that catalyze only the deamidation without touching peptide bonds at neutral pH regions. Bacillus circulans peptidoglutaminase was used for the deamidation of proteins. The enzyme was shown to have a very limited... 

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. 

Determination of the potential toxicity of alkali-treated protein as regards LAL action, therefore, may require measurement of the amount of lysinoalanine hydrolyzed by digestive proteolytic enzymes. This measurement requires a method that ... 

Racemization reactions also lead to protein cross-linking reactions. These reactions occur because of the formation of cross-linking compounds such as lysinoalanine (LAL). The formation of LAL not only renders the Lys that participates in the reaction unavailable to the animal, but it also decreases the digestibUity of total protein and other AA because LAL impairs the approach of proteolytic enzymes to the peptide chain (Boschin et al, 2003). However, because LAL formation occurs more readily at a higher pH, this reaction is more prevalent in alkali treated proteins compared with proteins simply exposed to heat treatments (Bunjapamai et al, 1982). Lysinoalanine content of a feed can be determined when analyzing feeds for AA content. 

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