The activity of 3-hydroxy-3-methylglutaryl-coenzyme A reductase (hydroxymethylglutaryl-CoA reductase) was considerably inhibited during incubation with ATP + Mg2+. The inactivated enzyme was reactivated on further incubation with partially purified cytosolic phosphoprotein phosphatase. The inactivation was associated with a decrease in the apparent Km of the reductase for hydroxymethylglutaryl-...

Renal Na-K-ATPase activity changes adaptively in response to chronic alterations in sodium reabsorption or potassium secretion, but the role of this enzyme in rapid adjustments of renal tubular Na and K transport is not known. To evaluate this question, microsomal Na-K-ATPase specific activity and kinetics were determined in the rat and guinea pig kidney after massive but short-term (3 h) sodiu...

Under anaerobic conditions the addition of reduced diphosphopyridine nucleotide to stoichiometric amounts of microsomal cytochrome reductase yields reduced flavin and a nucleotideenzyme complex characterized by a 315-rnp absorption peak (2). The properties of the reactive sulfhydryl groups of the enzyme and the evidence for the participation of only one such group in this reaction have been des...

The subcellular distribution of arylamidases in rat liver and rat kidney was studied. Lysosomes prepared from both tissues had the highest concentration of arylamidases. Different types of arylamidases have been found in the lysosomes and microsomes of these tissues. The lysosomal enzymes were inhibited by divalent metal ions, lost activity on storage, were inhibited by p-chloromercuribenzoate,...

Several substances have been shown to affect hepatic heme synthesis in the rat liver. Phenobarbital and the polycyclic hydrocarbon, 3,4-benzpyrene, produce an induction of aminolevulinic acid synthetase (ALAS), the enzyme mediating the first step in heme synthesis. This is followed sequentially by increased incorporation of glycine into microsomal heme, increased microsomal protoheme, cytochrom...

In earlier work (1) a DPNH’-specific microsomal cytochrome reductase, liberated by alcohol extraction and partially purified, was identified in liver microsome fractions from rats and rabbits. Microsomal cytochrome, but not cytochrome c, was found to act as electron acceptor in the oxidation of DPNH catalyzed by the enzyme. Through a rapid cytochrome to cytochrome reaction, cytochrome c was red...

The effects of three different enzyme-inducing agents (phenobarbital, 3-methylcholanthrene and rifampicin) on plasma and liver microsomal fraction paraoxonase and arylesterase were studied in rats. Although phenobarbital and 3-methylcholanthrene each increased the esterase activities in microsomal fraction, only 3-methylcholanthrene was capable to increase them in plasma. By contrast, the admin...

Detailed studies on the hydrolysis of p-acetylphenyl sulphate and oestrone sulphate by rat liver preparations strongly indicate that arylsulphatase C and oestrogen sulphatase are the same enzyme. Liver is the richest source of both enzymes, which have identical intracellular distributions, being localized mainly in the microsomal fraction. Low oestrogen sulphatase and arylsulphatase C activitie...

Tryptophan pyrrolase, the enzyme that catalyzes the oxidation of tryptophan to formylkynurenine, has been localized in the 11,000 X g supernatant fraction of mammalian liver homogenates (l), which contains microsomes and cell sap. In the course of the present investigations (Z), it was observed that the isolated microsomal fraction of rat liver is devoid of this enzyme. However, addition of thi...

1. The detergent Triton X-100 activates UDP glucuronyltransferase from rat liver in vitro six- to seven-fold with p-nitrophenol as substrate. The enzyme activity when measured in the presence of Triton X-100 is increased significantly by pretreatment of male rats with phenobarbital for 4 days (90mg/kg each day intraperitoneally). If no Triton X-100 is applied in vitro such an increase could not...