STUDIES ON THE MODIFICATION OF CASEIN BY MEANS OF THE PLASTEIN REACTION

Experiments have shown that covalent binding of amino acid ethyl ester (Met-, Ser-, and PSer-OEt) to caseinopeptides is possible by means of the plastein reaction and also in the course of simple proteolysis. T he properties of plasteins obtained with pancreatin as a physiological enzyme system differ markedly from serine proteinase plasteins reflec ting the influence of peptidases on plastein formation. Proteolysis-re sistant peptides are concentrated within pancreatin plasteins, which c onsist to two thirds of hydrophobic amino acids especially tyrosine (a pprox. 35 Mol %). One-phase and two-phase pancreatin plasteins exhibit almost identical functional and structural properties. Differences in the distribution of peptide molecular weights are particularly appare nt. In the two-phase system (ethanol/water) plastein material with a m olar mass > 5000 g/mol is formed, that is not dissolved by 8 mol/l ure a or by boiling in solutions containing SDS- and dithiothreitol.