Reverse micelles as a tool for elucidating the conformation of protamines in sperm-head nucleoproteins of some fish

Model polypeptides with amino acid sequences occurring in the components of clupeine and salmine were solubilised in reverse micelles of the system sodium bis(ethylhexyl) sulfosuccinate (AOT)—H₂O—iso-octane at [H₂O]/[AOT] ratios, w₀, of 4 and 10 for studying their conformation by circular dichroism (CD). The CD spectra were run between 200 and 300 nm. In the case of (Arg—Ala)_n the CD spectra obtained are typical of those for the α helix whereas those of (Arg—Gly)_n with n ≈ 15 are like random-coil spectra. The CD spectra of the sequential polypeptide (Arg₃—Gly)_n are typical of the α helix, in contrast to (Arg₃—Pro)_n. In the series (Arg_m—Ser)_n with m = 1, 2, 3, 4 and n = 15, 8, 5, 3, only the polymer with m = 2 appears to exist in the α-helical conformation.

It is concluded that the protamines studied attain an α-helical conformation only in the C-terminal region with an extended conformation in the central and N-terminal regions.