S U M M A R Y The cellular localization of protein tyrosine phosphatase 51 (PTPIP51) and its in vitro interacting partner protein tyrosine phosphatase 1B (PTP1B) was studied in human placentae of different gestational stages. The expression of PTPIP51 protein and mRNA was observed in the syncytiotrophoblast and cytotrophoblast layer of placentae from the first, second, and third trimesters. In contrast, PTP1B expression was restricted to the syncytiotrophoblast during all gestational stages. Cells of the cytotrophoblasts and parts of the syncytiotrophoblasts expressing high amounts of PTPIP51 were found to execute apoptosis as shown by TdT-mediated dUTP-biotin nick end labeling assay, cytokeratin 18f, and caspase 3 expression. PTPIP51 could also be traced in the endothelium and smooth muscle cells of placental arterial and venous vessels, identified by double immunostainings with antibodies directed against van Willebrand factor and a-smooth muscle actin. Some of these cells showing a high PTPIP51 reactivity were Ki67 positive, indicating proliferation. Additionally, a small population of placental CD14-positive macrophages and mesenchymal cells within the villous stroma were detected as PTPIP51 positive. Our data suggest that both proteins, PTPIP51 and PTP1B, play a role in differentiation and apoptosis of the cytotrophoblast and syncytiotrophoblast, respectively. Moreover, PTPIP51 may also serve as a cellular signaling partner in angiogenesis and vascular remodeling. (J Histochem Cytochem 57:143-153, 2009)
The mechanism of action and the regulatory properties of glutamate dehydrogenase from pea seedlings (Pisum sativum, var. Späths Violetta) have been investigated by using a highly purified preparation of the enzyme. Kinetic experiments show that the binding of the coenzyme (NAD(+) or NADH) and the substrate (L-glutamate or α-ketoglutarate) is sequential. The formation of a quarternary complex with ammonia as additional substrate is questionable, as can be seen from the kinetic data. The anions of the ammonia source have a strong rate-regulating effect on the NADH reaction. The adenosinphosphates AMP, ADP, and ATP exert an inhibiting effect on both the reductive amination and the oxidative deamination reaction. The former reaction is inhibited half as much as the latter. Dead end inhibition offers a sufficient explanation for this effect. The glutamate dehydrogenase from pea seedlings is not regulated by the energy charge. Zn(2+) ions are strong inhibitors of the NADH-reaction; their inhibitory effect on the activity is indirect and can be reversed by addition of ATP. A reaction sequence is formulated.
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