| Popis: |
Lysinoalanine formation in lactalbumin, casein and soya protein was studied as a function of pH, temperature and time. Formation was very rapid at elevated temperature and pH. At 90°C and pH 12 or 10, lysinoalanine levels in excess of those previously reported to cause nephrocytomegaly in rats were observed after only a few minutes of treatment. No detectable lysinoalanine was formed at slightly acidic pH values. Under very severe treatment conditions (pH 12, 90°C), lysinoalanine was formed very rapidly but was apparently destroyed upon further exposure. Lysinoalanine formation in a solution of polylysine with polyserine demonstrated both that unsubstituted serine served as a precursor to lysinoalanine formation and that significant interpeptide crosslink formation occurred under the conditions studied. Studies with model proteins and peptides supported the idea that cystine residues were the primary precursors of the lysinoalanine crosslink under moderately alkaline conditions, but that serine became a more important contributor as the severity of the alkaline treatment increased. |
