The Disulfide Bonds of Egg White Lysozyme (Muramidase)

Abstract

The availability of the amino acid sequence of egg white lysoeyme makes it possible to identify the pairing of the 8 half-cystine residues that give rise to the four disulfide bonds present in the native protein (1,2). In establishing the positions of the disulfide bonds in insulin (3, 4) and ribonuclease (5, 6) it was shown that disulfide interchange, which occurs under certain experimental conditions, may lead to factitious pairing of halfcystine residues. The studies on lysozyme reported here were designed to minimize this hazard, particularly since data from the peptic digestion of native lysozyme published earlier (7) were in direct conflict with those of Jolles, who reported that a disulfide bond exists between half-cystines I and II (8, 9). In view of this disagreement, and in view of other conflicting data concerning the amino acid sequence of this protein (1, 2), all of the peptides resulting from the peptic digestion of native lysozyme have been examined, and, where pertinent, either the disultide bonds have been identified or further sequence studies have been performed. During the course of these studies, a new method of establishing the positions of disulfide bonds in proteins has been applied to lysozyme by Brown (lo), and his results are in complete agreement with those reported here. In their most recent publication, Jolles, Jauregui-Adell, and Jolles (11) give a pairing of halfcystine residues which is different from that reported earlier (8, 9) and is the same as those described in this communication.