Homologous structural domains in chicken egg-white ovomucoid: Characterization and acid denaturation.

ABSTRACT

The primary structure of ovomucoid shows considerable sequence homology at three contiguous regions which form structural domains I, II and III. In order to see whether or not the three domains fold similarly and acquire similar overall native conformation/shape, two fragments A and C were obtained by controlled peptic digestion of ovomucoid. The two fragments were investigated for their chemical composition, molecular weight, anti-tryptic activity, hydrodynamic behaviour, optical properties and acid denaturation. Results on molecular weight, amino acid composition and inhibitory acitivity show that the fragments A and C correspond respectively to domain I-II and domain III. Optical data suggested more exposure of tyrosine residues in the fragments than in the intact molecule. Domain III exists in a compact and globular conformation under native conditions whereas domain I-II and ovomucoid appear to possess asymmetric conformation. Results on acid denaturation show that the process is thermodynamically reversible and that inter-domain separation probably precedes denaturation of domains during acidification of ovomucoid.