Zinc and magnesium in the uterus of the pregnant and pseudopregnant mouse and the effects of Mg2+ ions on uterine alkaline phosphatase.
The levels of zinc and magnesium in the mouse uterus during early pregnancy and pseudopregnancy were determined using atomic absorption spectroscopy techniques. The total zinc and magnesium content of the uterus increased between days 5 and 12 of pregnancy and between days 5 and 9 of content of the pseudopregnancy when decidual cells were present. However, the metals were not accumulated at a rate sufficient to match increases in uterine weight and constant concentrations (micrograms of metals per gram wet weight ot tissue) were not maintained over the various reproductive stages studied. The accumulation of the metals was associated with the presence of decidual cells, and non-decidualized horns of pseudopregnant mice failed to increase their total content of zinc and magnesium between days 5 and 9. The magnesium content of each uterus was usually between 5- and 13-fold greater than the total zinc content. mg2+ in low concentration (0-2mM) stimulated both the pyrophosphatase and orthophosphatase activities of purified preparations of the mouse uterine metalloenzyme, alkaline phosphatase. Higher concentrations (up to 8 mM) of the cation decreased pyrophosphatase activity but did not alter orthophosphatase activity. Mg/+ was more effective, however, in increasing the orthophosphatase activity of the enzyme and its stimulating effects in this case were greater in carbonate-bicarbonate buffer than in glycine-NaOH buffer. Mg2+ did not significantly influence apparent Km values or the response of the enzyme to changes in temperature. Zn2+, however, was required to maintain the stability of alkaline phosphatase apoenzyme preparations. It was concluded that during normal pregnancy and pseudopregnancy zinc and magnesium would always be present in amounts considerably greater than those required to saturate alkaline phosphatase for full catalytic activity. Thus, while the metals exert major effects on the activity and stability of the enzyme in vitro, they may not be major factors involved in the in utero regulation of the enzyme during early pregnancy.
D000469:Alkaline Phosphatase / Q000378:metabolism*; D000818:Animals; D005260:Female; D007700:Kinetics; D008274:Magnesium / Q000032:analysis* / Q000494:pharmacology; D051379:Mice; D008815:Mice, Inbred Strains; D011247:Pregnancy; D011270:Pregnancy, Animal; D011555:Pseudopregnancy / Q000378:metabolism*; D014599:Uterus / Q000378:metabolism*; D015032:Zinc / Q000032:analysis*
D000469:Alkaline Phosphatase; D008274:Magnesium; D015032:Zinc