Keratinization of rat vaginal epithelium IV. Modulation of transglutaminase activity by oestradiol

Calcium-dependent transglutaminase activity was found to be present in vaginal homogenates from adult cycling rats. Treatment of immature or adult ovariectomized rats with oestradiol (0.1 μg/g body weight) resulted in 1.5–2-fold enhancement in the enzyme activity. Progesterone treatment (0.1 μg/g body weight) decreased the enzyme activity. Analysis of amino acids produced by proteolytic enzyme digestion of insoluble keratins from rat vaginal tissue indicated the presence of γ-glutamyl-ε-⥿sine dipeptide (4 μmol/g protein) in this protein. These results suggest that oestradiol acts on vaginal tissue and induces the activity of transglutaminase. This enzyme catalyses the formation of γ-glutamyl-ε-lysine crosslinks between keratin polypeptides and thus leads to kerartization of the tissue.