Synthesis of two peptide mimetics as markers for chemical changes of wool's keratin during skin unhairing process.

The sheep skins unhairing process with preliminary alkaline treatment of the wool leads to two unnatural dipeptide mimetics lysinoalanine (Lys(*) - Ala) and ornithinoalanine (Orn(*)- Ala) obtaining. They are result from the keratin hydrolysis process. The changes of wool keratin make it resistant to sulphide degradation. We synthesized and characterized these unnatural dipeptides under the experimental conditions. The structures and mechanism of Lys(*) - Ala and Orn(*)- Ala obtaining were elucidated. The using of newly synthesized products as markers for control of wool's keratin changes during skin unhairing process was demonstrated. The developments have also been the result of economic and environmental pressures to meet environmental regulations.

Formation of lysinoalanine during heat treatment of milk.

The heat-induced formation of lysinoalanine (LAL) was studied in raw skim milk that had been subjected to heat treatments as is usual in milk technology. Preheat treatment of milk at temperatures below 100 degrees C up to 20 min resulted in neglectable LAL amounts below 10 ppm i.p. (i.p.=in the protein) if at all. Tests with an UHT pilot plant showed that there was no proven formation of LAL with direct UHT-treatment at 110-130 degrees C for 10-25 min. In indirect UHT-treated milk vert small LAL amouints up to 50 ppm i.p. were detected only in those milk samples that were treated at temperatures high than 145 degrees C and holding times longer than 10 s. Autoclave sterilization in the range of 110-129 degrees C/10-25 min induced LAL amounts of 110 to 710 ppm i.p.. LAL formation in autoclave sterilized milk was almost directly dependent on heating temperature and time. Pre-treatment at temperatures below 100 degrees C induced no further LAL formation in any sterilization processes subsequent to preheating. In the pH range 6,50-6,90 LAL amounts in autoclave-sterilized milk increased directly with higher pH values at all temperatures. The varying degree of LAL formation with pH value was substantially more noticeable at higher than at lower temperatures. Increasing of lactose concentration caused only an insignificant decrease in LAL formation in autoclave-sterilized milk.

Lysinoalanine as a metal chelator. An implication for toxicity.

Synthetic lysinoalanine (N epsilon-DL-(2-amino-2-carboxyethyl)-L-lysine) was found to have a strong chelating ability for metals. It became colored when mixed with Cu+2 and showed absorption characteristics typical of a complex. Lysinoalanine could inactivate metalloenzymes such as carboxypeptidases A and B and yeast alcohol dehydrogenase, by removing the zinc ion from the active site. Model building for a mononuclear complex of the metal and lysinoalanine with space-filling models was possible for the LD-isomer, N epsilon-D-(2-amino-2-carboxymethyl)-L-lysine. Etiological studies of its toxicity to humans should be made because the chelating ability of lysinoalanine is sufficiently strong to remove the metal from the enzyme active center at millimolar concentration.

Inhibition of lysinoalanine synthesis by protein acylation.

Treating wheat gluten, soy protein, and lactalbumin under alkaline conditions at 65 degree C for various times destroys part of the threonine, cystine, lysine, tyrosine, and arginine residues in these proteins. The losses were accompanied by the appearance of lysinoalanine and unidentified ninhydrin-positive substances. Treating wool under somewhat milder alkaline conditions destroys part of the cystine and lysine residues, but not the other amino acids cited. In this case, loss of cystine and lysine was accompanied by the appearance of lanthionine and lysinoalanine. Amino acid analysis of alkali-treated acylated proteins revealed that acylation by acetic and succinic anhydrides prevents or minimizes destruction of lysine residues and the formation of lysinoalanine in wheat gluten and soy protein and, in wool, minimizes destruction of cystine and lysine residues and the formation of lanthionine lysinoalanine. Mechanisms are proposed to explain the observed inhibiting effects of protein acylation and oertain additives on lysinoalanine formation.