STRUCTURAL CHARACTERIZATION OF THE MOLTEN GLOBULE AND NATIVE STATES OF OVALBUMIN - A H-1-NMR STUDY

Molecular characteristics of ovalbumin (OVA) in the acidic (pD 3.08, t he E-form) and neutral [pD 7.29, the N-form (native form)] regions wer e studied by measuring effective radii, H-1 NMR spectra, spin-echo H-1 NMR spectra and cross-relaxation times (T-IS) from irradiated to obse rved protein protons which are particularly sensitive for detection of the mobile segments and/or structural looseness in proteins. H-1 NMR spectra did not show significant differences between the N-and E-forms except for the spectral lines in the CH3, epsilon CH2 and aromatic re gions. Effective radii and T-IS values for main-and side-chains showed 1.08 and 1.5- to 2.0-fold increases on going from the N- to E-forms, respectively. The elongation of T-IS values might indicate the appeara nce of the fluctuating tertiary structure in the E-form. Molecular cha racteristics of the E-form, inferred from reported far ultraviolet-cir cular dichroism (UV-CD) spectra in the peptide region, near UV-CD spec tra in the aromatic region [Koseki et al. (1988) J. Biochem. 103, 425- 430], effective radii and especially elongation of T-IS values might i ndicate that the E-form could be in the molten globule state. The onse t of denaturation of OVA using T-IS measurements was also studied. (C) Munksgaard 1997.