[Thymidylate synthetase in the antimesometrial and mesometrial portions of decidual tissue under normal conditions and following application of the antifolate preparation chloridine].

Specific activity of thymidylate synthetase (TMS) under normal conditions and after the action of pyrimethamine was investigated in antimesometrial (A) and mesometrial (M) parts of rat decidua. On the 9th-11th days of pregnancy specific activity of TMS in the A part proved to be higher than in the M part of decidua, and the former one reached its maximum by the 10th day. Specific activity of TMS in the M part decreased gradually from the 9th to 11th days of gestation. Pyrimethamine, applied on the 9th day of pregnancy caused a wave-like increase in the specific activity of TMS in the A part; this elevation was not so pronounced in the M part; A study of the physico-chemical properties of TMS from the decidua and the embryos of rats showed that the enzyme had a molecular weight of 58000, an optimal pH of 6.9, and could be quickly inactivated by heating.