Primary structure of the protamine isolated from the sperm nuclei of the dog-fish Scylliorhinus caniculus.

A protamine was isolated from mature sperm nuclei of the dog-fish Scylliorhinus caniculus. It contains 31 amino acids per molecule and only five types of residues: arginine (20), glycine (6), serine (3), alanine (1) and tyrosine (1). The primary structure of this protamine is reported. The N-terminal sequence contains the four hydroxylated amino acids of the molecule; the C-terminal region shows a sequence of eleven adjacent residues of arginine and contains all the glycine residues present in the protein. The structure of this 'scylliorhinine' is compared to the amino acid sequence of other sperm protamines whose structure has been previously published. The presence of a modified tyrosine residue in some preparations is discussed in relation to sperm maturation.