Hybrid clones segregating human chromosomes were prepared by fusing mouse RAG cells to fresh human bone marrow cells and tested for the mixed-function oxygenase [flavoprotein-linked monooxygenase; RH, reduced-flavoprotein:oxygen oxidoreductase (RH-hydroxylating); EC 1.14.14.1] arylhydrocarbon hydrocarbon hydroxylase. Neither constitutive nor induced aryl hydrocarbon hydroxylase activity was det...

The urinary level of N-acetyl-beta-D-glucosaminidase (NAG) was reported to be a useful marker for the assessment of renal function. This enzyme was also detected at a high activity in seminal fluid. In our preliminary report, seminal NAG activity was 1,000 times higher than urinary NAG level in healthy volunteers. Moreover, the fraction ratio A to B isozymes was changed in seminal fluid indepen...

Adenylyl cyclase superactivation, a phenomenon by which chronic activation of inhibitory Gi/o-coupled receptors leads to an increase in cAMP accumulation, is believed to play an important role as a compensatory response of the cAMP signaling system in the cell. However, to date, the mechanism by which adenylyl cyclase activity is regulated by chronic exposure to inhibitory agonists and the natu...

The polymorphic acetyltransferase isozyme expressed in homozygous rapid acetylator inbred hamster liver cytosol was purified over 2000-fold by sequential Q-Sepharose fast-flow anion-exchange chromatography, Sephacryl S-200 high-resolution size-exclusion chromatography, Mono Q anion-exchange fast-protein liquid chromatography, and preparative polyacrylamide gel electrophoresis. The isozyme migra...

The COZ hydration and HC03dehydration activities of human red cell carbonic anhydrase isozymes B and C (HCAB and HCAC) have been studied as a function of temperature from 0” to 37°C. The Arrhenius plots of In kcat versus 1/T are linear for both isozymes in both hydration and dehydration reactions, indicating that the rate-determining steps remain unchanged over this temperature range. The 37°C ...

Background: CKMB, the cardiac-specific heterodimer of cytosolic creatine-kinase (CK), is developmentally and physiologically regulated, tissue hypoxia being a proposed regulator. In patients with cyanotic heart disease the myocardium is perfused with partially saturated blood. We questioned whether the myocardium of cyanotic subjects contains higher proportions of CKMB. Materials and Methods: C...

Senecionine (SEN) is a representative of the hepatotoxic pyrrolizidine alkaloids. Although phase I metabolism for cytochrome P450-mediated metabolic activation of SEN was investigated extensively, phase II metabolism for glucuronidation of this compound has not been investigated until now. In our present study, one unique glucuronidation product of SEN in human liver microsomes (HLMs) was ident...

We describe the kinetics of pentoxifylline formation from lisofylline in human liver microsomes using selective inhibitors of cytochrome P450 isozymes, correlation studies with specific isozyme activities, and cDNA-expressed human CYP1A2 and 2E1. A biphasic model fitted the data best for the formation of pentoxifylline, Km1 = 0.282 +/- 0.135 microM, Vmax1 = 0.003 +/- 0.001 nmol/min/mg protein, ...

The in vitro N-hydroxylation of guanabenz as well as the corresponding N-dehydroxylation of guanoxabenz has been previously detected in biotransformation studies with microsomal fractions of different species including human hepatic microsomes. Furthermore, the N-hydroxylation of guanabenz was found to be catalyzed by enriched cytochrome P450 (P450) fractions in reconstituted systems. Strong co...