Kinetics of prostacyclin synthetase in umbilical artery microsomes from normal and pre-eclamptic pregnancies.

1 Prostacyclin synthetase in umbilical artery microsomes obeys Michaelis-Menten kinetics. 2 The maximum velocity (Vmax) of prostacyclin synthetase prepared from normal umbilical arteries was significantly higher than the Vmax of prostacyclin synthetase in umbilical arteries taken from pre-eclamptic pregnancies. 3 The Michaelis-Menten constant (Km) of the two prostacyclin synthetase preparations was significantly different with the synthetase from pre-eclamptic arteries have a higher affinity for substrate. 4 The limiting factor for prostacyclin synthesis is Vmax at high substrate concentrations which appears to be the case in umbilical arteries. However, at low substrate concentration there would be no difference in prostacyclin synthesis by the two forms of prostacyclin synthetase.