Structures determination of biological peptides generated by hydrolyzation of modified milk casein

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Casein after reaction with glucose was dialyzed against water, freeze dried and used as modified casein. The modified degree of lysine residue was about 50%. The modified casein was then hydrolyzed by pepsin-pancreatin, and isolated into three fractions of under 3,000Da, 3,000-10,000Da and over 10,000Da. The yield of 3 peptides fractions were 75%, 5% and 19% respectively. In comparison with native casein, the peptides under 3,0000Da from modified casein was deceased about 20%. The results by HPLC showed that there is clear difference between the peptides pattern of native casein and modified casein. Moreover, three special peptides were generated from modified casein. The quantity of peptides inhibit Angiotensin converting enzyme, from modified casein was also decreased.Besides, RDMPI peptide from beta-Casein structure was also synthesized. This peptide was reacted with glucose, at 110℃ for 2 h. The following was made clear: (1) HPLC pattern of native peptide and modified peptides was clearly different, it seemed that peptide No 1,2,3,4,5,6 were gycated. (2) By the MS analysis, peptide No 5 was glycated, and, peak was also contained RDMPI+1G and RDMPI+2G. (3) By the analysis of Protein Sequencer, the glycation of Nterminal Arginine residue of RDMPI was observed.