High‐field magnetic birefringence study of the structure of rodlike phages Pf1 and fd in solution

Abstract

Abstract The magnetic orientation of the rodlike bacterial viruses Pf1 and fd in dilute aqueous solution was detected by high‐resolution birefringence measurements. Partial alignment takes place parallel to the magnetic field chiefly due to the diagmagnetic anisotropy of the highly ordered α‐helices in the coat protein. It follows from the analysis of the experimental diamagnetic anisotropy that in both phages the α‐helices and aromatic amino acids are oriented relatively parallel to the phage axis. In Pf1 these become, on average, more nearly parallel as the temperature is reduced from about 25 to 5°C. These results demonstrate that high‐resolution magnetically induced birefringence measurements can be used to investigate some general structural features of complicated biological particles in solution.