Sodium dodecyl sulfate-bovine plasma albumin complex. Structural transition from native to relatively compact globule forms with mobile side chains in acidic region--N-F transition.

The acid-induced isomerization (the N-F transition) and expansion of sodium dodecyl sulfate-bovine plasma albumin complex (ADm; m, molar ratio of added sodium dodecyl sulfate to bovine plasma albumin; O less than or equal to m less than or equal to 12) were studied by measuring CD-resolved secondary structure, fluorescence polarization and life-time of tryptophyl fluorophors, acid-titration with the electrostatic correction for the surface potential, 1H-n.m.r. spectra and cross relaxation time between irradiated and observed protons. The immobilization of tryptophyl fluorophors observed in the F-form of AD0 was suppressed in the F-form of AD10. The acidtitration analysis of AD12 showed non salt-bonding between carboxylate groups and cationic side chains in the F-form, as in the case of AD0, indicating charged side chains being presumably mobile. 1H-n.m.r. spectra and cross relaxation times between irradiated and observed protons in the F-form of AD10 indicated the increase in the local motion. On the other hand, AD10 and AD12 did not show any significant change in the CD-resolved secondary structure in the N-F transition region. The F-form of AD10 or AD12 may therefore be the moltenglobule state which has secondary structure similar to the N-form of the complexes with fluctuating tertiary structure (side chains).