Reactivity of the Tryptophan Residues in Lysozyme

Abstract

REPORTS have recently been published on the nature of the tryptophan residues in hen's egg white lysozyme and the relation of these residues to enzymatic activity. Hartdegen and Rupley¹ showed that the oxidation of a single tryptophan residue with iodine results in the loss of enzymatic activity. Hachimori et al.² have oxidized the tryptophan residues of lysozyme with hydrogen peroxide, concluding that all the tryptophans in lysozyme are relatively refractory toward oxidation and that the destruction of 1.4 mole of this amino-acid per mole of the enzyme results in the loss of 95 per cent of the lytic activity. Hamiguchi and Kurono³ have examined the effect of 2-chloroethanol on the secondary structure of lysozyme; they reported that when the enzyme is treated with solvents varying in composition from 0 to 32 per cent 2-chloroethanol (v/v), there are spectral changes indicating the disruption of hydrophobic regions and the exposure of buried tryptophan residues, although the optical rotatory dispersion investigations show no alteration, of helix content. Only at higher concentrations of 2-chloroethanol does the helix content increase.