Creatine kinase activity in human endometrium: relative distribution in isolated glands and stroma.

Creatine kinase (CK) activity was measured in human endometrium as a function of the normal menstrual cycle. The specific activity of CK was consistently higher in the secretory endometrium than in the proliferative tissue (proliferative, 0.9 U/mg of protein; secretory, 3.3 U/mg of protein). The relative distribution of CK activity in isolated glands and stromal cells was determined following collagenase digestion of the endometrial specimen according to our previously described procedure. These studies show an enrichment of CK activity in the glands that is greater than fivefold that present in the stromal cells. Electrophoretic mobility of CK activity on cellulose acetate further indicates that the endometrial enzyme is a BB (brain type) isoenzyme. In the rat uterus, CK has been shown to be an estrogen-induced protein. In contrast, the activity of this enzyme may be modulated by progesterone in human endometrium.