[Changes in the secondary structure bacteriophage T4 envelope protein after its polymerization]

Circular dichroism (CD) spectra of the structural protein of the bacteriophage T4 sheath (gp 18) in a monomeric native state, helices, polysheaths and contracted sheaths were measured in the range 184-310 nm. The secondary structure of the protein studied was calculated from the spectra in the range 190-240 nm according to Provencher and Glöckner. It has been shown that the polymerization is proceeded without change of the alpha-helical content in the secondary structure of gp 18: estimated alpha-helix in monomeric gp 18, helices and polysheaths was 39%. The beta-form content in monomeric gp 18, helices and polysheaths was 33, 32 and 37%, respectively. Tail sheath contraction is attended by a 14% decrease in gp 18 alpha-helicity and a 5% increase in its beta-form content.