Solution behavior, circular dichroism and 220 MHz PMR studies of the bovine myelin basic protein

Abstract

Bovine myelin basic protein has been investigated with regard to its solution behavior, circular dichroism and 220 MHz PMR spectral properties.At pH 4.8 [gamma]/2 = 0.1 acetate buffer, light scattering yielded a Mr of 17 700 and a virial coefficient of 1.0[middle dot]10-4 mol[middle dot]ml/g2. Above pH 7.0 the protein was found to aggregate to higher mol. wt species.Sedimentation experiments at pH 4.8 yielded s[deg]20,w of 1.27 S at [gamma]/2 = 0.1 and 1.46 S at [gamma]/2 = 0.35. The diffusion coefficient determined from ultracentrifugal experiments was 7.25[middle dot]10-7 cm2/s at [gamma]/2 = 0.1 and 0.35. The value of [function of (italic small f)]/[function of (italic small f)]0 from diffusion at pH 4.8 and [gamma]/2 = 0.35 was 1.64, corresponding to an axial ratio of 11 to 1. The radius of gyration was calculated as 4.28 nm and the root mean square end to end distance was 10.5 nm. At pH 9.0, [gamma]/2 = 0.1, s[deg]20,w was 1.71 S and D[deg]20,w was estimated at 7.4[middle dot]10-7 cm2/s. The behavior at pH 9.0 reverted to the behavior at pH 4.8 when the pH was readjusted. The E1cm1% = 5.64 at 276.4 nm and 225 at 196 nm.Titration of the protein with trifluoroethanol elicited three distinct regions of conformational stability having increasing helical content as the mol fraction of trifluoroethanol increased.The results of the present study have permitted some comparison of analogous properties and conformational behavior with the basic membrane protein cytochrome c.