IDENTIFICATION OF PHOSPHOSERYL RESIDUES IN PROTAMINES FROM MATURE MAMMALIAN SPERMATOZOAL

Protamines isolated from ejaculated human, stallion, bull, boar, and r am spermatozoa were subjected to phosphoserine conversion reaction and protein sequencing. Phosphoserines were detected as S-ethylcysteines. Endogenously phosphorylated protamines have previously been found onl y in ejaculated human sperm. In this study, we demonstrate that ejacul ated sperm from other species also contain protamines phosphorylated a t serine residues. In P1-protamines, the endogenously phosphorylated s erines were located at the N-terminal region in all species studied, w hereas in major forms of human and stallion P2-protamines, the serine residues located in the middle region of the molecule were predominant ly phosphorylated. These results support the current DNA binding model in the case of the P1-protamines. The internal location of the phosph orylated serines in the P2-protamines indicates, however, that the bin ding of these proteins to DNA or their interaction with other protamin e molecules may differ from that of P1-protamines. This also suggests that, during sperm maturation, P2-protamines may have a role different from that of P1-protamines.