Male Donryu, Wistar King rats showed discontinuous variations in hepatic microsomal UDP-glucuronyltransferase activities towards androsterone, but not towards testosterone, bilirubin, phenolphthalein and 4-nitrophenol. Fresh microsomal fraction with a low transferase activity towards androsterone formed 0.049--0.080 nmole of glucuronide/min per mg of protein, whereas fresh microsomal fraction w...

A microsomal preparation from chick embryo cartilage has been shown to catalyze the incorporation of sulfate-36S from 3’-phosphoadenosine 5’-phosphosulfate-3% into microsomal glycosaminoglycan. This enzyme preparation is the same preparation that previously has been shown to catalyze the formation of chondroitin (nonsulfated) from sugar nucleotide precursors. The microsomal sulfate acceptor app...

Specific degradation of the phospholipid membrane of guinea-pig liver microsomal fraction with phospholipase A inactivated glucuronyltransferase. The inactivation was reversed by phosphatidylcholine and mixed microsomal phospholipid micelles at concentrations similar to those present in intact microsomal preparations. The other commonly occurring phospholipids did not reactivate phospholipase A...

Postnatal developmental changes in hapatic microsomal UDP-glucuronyltransferase were studied in the rat. The previously reported postnatal decline in the capacity of microsomal fractions to glucuronidate p-nitrophenol was found to be observable in unperturbed preparations only at non-saturating concentrations of the substrate UDP-glucuronic acid. At saturating concentrations of UDP-glucuronic a...

Testicular microsomal fraction (10,000•`105,000 •~ g precipitates) of adult rats which was responsible for enzymic transformation of pregnenolone into testosterone was inactivated by phospholipases C and D, but not by phospholipase A . After the 10 kilocycles/sec. sonication for 60 mins., most of the microsomal enzyme activities were still found in the 105,000 •~ g precipitates. The specific ac...

This study characterizes microsomal heme oxygenase, a previously undescribed enzyme which catalyzes the oxidation of heme at the cr-methene bridge to form biliverdin. This step is then coupled with soluble NADPH-dependent biliverdin reductase to form bilirubin; microsomal heme oxygenase is rate-limiting in this pathway. By all analytical criteria, the product of this reaction is bilirubin. Most...

The effect of binding of amitriptyline to human liver microsomes and to microsomes from human B-lymphoblastoid cells on the estimation of enzyme kinetic parameters describing N-demethylation to nortriptyline was investigated using a combination of microsomal binding and in vitro enzyme kinetic studies. Quantitative binding in both matrices increased with higher microsomal protein concentrations...

The kinetic properties of the rat liver microsomal ATPase, with respect to Na(+), K(+) and AT P requirements were examined. Presence of Na(+) and K(+), or both hardly caused any stimulation of the enzyme activity. The Km values for Na(+) and K(+) were substantially low (0.32 and 0.05 mM, respectively), compared to those reported for the Na(+), K(+) ATPasesfrom different tissues. Substrate kinet...

Sendai virions contain an enzyme which catalyzes the incorporation of ribonucleotides into ribonucleic acid (RNA). Enzyme activity was optimal at pH 8.0 and 28 C; otherwise conditions were similar to those reported for Newcastle disease virion (NDV) RNA polymerase. The initial rate of RNA synthesis by the Sendai virion enzyme was about 10 pmoles per mg of protein per hr, but after 3 hr of incub...