Behaviour and properties of membrane-bound mouse uterine alkaline phosphatase during early pregnancy

Most of the alkaline phosphatase activity in the mouse uterus during early pregnancy was found to be membrane-bound and was associated with particulate material when homogenates were centrifuged at 105 000 g. The activity of the enzyme increased in both the particulate and cytosol fractions of uterine homogenates during early pregnancy to reach maximum values on day 7 of pregnancy. Studies of the enzyme in its membrane-bound and cytosolic forms before and after solubilization with Triton X-100, and n-butanol failed to detect any evidence that the membrane microenvironment or membrane are deeply buried within the membranes of uterine cells. Thus, the properties of the enzyme in response to amino acids, inhibitors, and Mg2+ and Zn2+, and changes in pH, substrate concentration and temperature were essentially unaltered when the phosphatase was present in a membrane-bound or cytosolic form, or when fractions were treated with Triton X-100 and n-butanol. Solubilized preparations of the enzyme from particulate and cytosol fractions of uterine homogenates displayed zones of activity with similar anodal migration rates during electrophoresis on cellulose acetate membranes suggesting that the cytosolic activity may arise from particulate material during homogenization of the tissue. Several amino acids stimulated the activity of the phosphatase while cysteine, histidine, homoarginine, Na2HPO4 and 4-(p-aminophenylazo)phenylarsonic acid were inhibitory. In addition, Km values for the enzyme from all uterine fractions hydrolysing p-nitrophenyl phosphate were temperature-dependent.