Immunochemical and structural analysis of pepsin-digested egg white ovomucoid

Ovomucoid, an egg protein comprising similar to 10% egg white, was digested using the enzyme pepsin, and fragments were isolated by anion-exchange and reverse phase HPLC. Four distinct fragments were identified by analysis wi th SDS-PAGE, including three large fragments with molecular weights of arou nd 24, 18, and 14 kDa. N- and C-terminal and amino acid sequencing analyses identified the fragments as V-134-C-186 (domain 3), V-21-A(133), and A(1)- A(133) (domain 1 + 2). Further separation and sequencing of the fraction co mposed of small peptides, to determine their exact makeup and location in t he protein, remained to be carried out and identified a peptide G(51)-Y-73 All four fragments showed IgE-binding activity, as measured by ELISA, using human sera from egg-allergic individuals. Little change in the digestibili ty of ovomucoid by trypsin and chymotrypsin was observed following digestio n with pepsin, indicating that pepsin-digested ovomucoid retains its trypsi n (protease) inhibitor activities. Reduced carboxymethylated ovomucoid was prepared, and digestion with pepsin produced significantly more peptides th an did the digestion of the native ovomucoid, indicating that the disulfide bonds play a significant role in the digestive resistance of ovomucoid. Th e reduction of ovomucoid enhanced its digestibility and lower allergenicity of the protein.