Nuclear magnetic resonance of protamines. A carbon-13 relaxation study of the three main fractions of clupeine.

The 3 main fractions of clupeine, the protamine extd. from herring sperm, were investigated by 13C NMR techniques. The dynamic behavior, examd. through the evaluation of the spin-lattice relaxation times (T1) of individual C resonances assigned to both backbone and side chains, reveals interesting features. The relaxation times of backbone a-C, interpreted on the basis of an axially sym. ellipsoid, point to the clupeine fractions as being essentially extended in aq. soln. These times remain const. along the polypeptide chain and are of the order of 0.16 s. Conversely, the side chains show different flexibilities in the presence of monophosphate counterions, thus demonstrating a diverging behavior which may be biol. relevant. In particular, the side-chain flexibilities of fraction YI decrease, whereas those of fractions Z and YII are either const. or increase. Comparison of these data with the viscosity measurements helps in explaining the viscosity obsd. in the presence of phosphate.