The hepatic microsomal enzyme UDP-glucuronyltransferase undergoes a complex developmental pattern in which enzyme activity is first detectable on the 18th day of gestation in rats. Prepubertal activities are similar for males and females. However, postpubertal sexual differentiation of enzyme activity occurs in which male activities are twice those of females. Neonatal administration of testost...

Cholesterol 7 alpha-hydroxylase, the rate-limiting enzyme for bile acid synthesis, was shown to be copurified with human liver microsomal cytochrome P-450. When these cytochrome P-450 species were reconstituted in phospholipid-cholesterol vesicles together with NADPH-cytochrome P-450 reductase, high cholesterol 7 alpha-hydroxylase activity was obtained in the presence of NADPH. The activity rep...

has previously been isolated by Horecker (1) from an acetone powder of liver and characterized as a flavoprotein. It was initially suggested that this enzyme was localized in hepatic mitochondria. However, subsequent studies have revealed that triphosphopyridine nucleotide-cytochrome c reductase activity is also present in hepatic microsomes (a), and it has been reported that the properties of ...

The inhibition of several enzyme activities by free fatty acids has been examined. The inhibition of rat liver microsomal linolenate-activating enzyme activity by linolenate was found to be due to the inactivation of enzyme by substrate fatty acid. Stearoyl coenzyme A was also found to inhibit linolenate-activating enzyme. Likewise, microsomal glucose 6-phosphatase was inhibited by oleate; the ...

The basic properties of estradiol 2-hydroxylase in rat brain microsomes were studied and compared to the known characteristics of rat liver microsomal estradiol 2-hydroxylase. Rat liver microsomal estradiol 2-hydroxylase, which has been considered to be a cytochrome P450-like enzyme, was largely inhibited by carbon monoxide. On the other hand, the effect of carbon monoxide on the activity of ra...

The metabolic activation of the prohormone vitamin D(3) requires a 25-hydroxylation that has been reported to be catalyzed by both mitochondrial CYP27A and a microsomal vitamin D(3) 25-hydroxylase in the liver. CYP27A has been extensively studied, but its role as a physiologically important vitamin D(3) 25-hydroxylase has been questioned. The present paper reports that the microsomal vitamin D(...

Paraoxon, the main active metabolite of the organophosphorus insecticide parathion, exerted a dose-dependent inhibitory effect on the activity of pig kidney (Na+ + K+)-ATPase contained in microsomal fraction and purified from it. Substrate kinetics studies revealed the existence of two active sites with high and low affinity to ATP. The Dixon analysis of the mode of the inhibition indicated its...