Conformational Changes Induced by Ionic Strength and pH in Two Bovine Myelin Basic Proteins

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Abstract
The structures of 2 biologically different myelin proteins, A1 from the CNS and P2 from the peripheral nervous system, were investigated. Both proteins were isolated from nerve tissues. Conformational changes in the homogeneous proteins were examined in aqueous solutions by circular dichroism measurements. The secondary structures of both proteins were very stable between pH 2.5-11.7. Unlike the P2 protein, the A1 protein was stable up to pH 13 without detectable conformational changes. The stereochemistry of the polypeptide chains of both proteins was markedly different in the presence of urea. While the value of .THETA.222 for the A1 protein changed linearly with increasing urea concentration, a sigmoidal curve was obtained for the P2 protein. The observed differences in the dichroic properties of the basic myelin proteins A1 and P2 indicate the possibility of further structure-function correlations.