Pentane was measured in a mixture of guinea pig liver microsomes and carbontetrachloride (CCl4) in the presence of nicotineamide adenine dinucleotide phosphate (NADPH) and under anaerobic conditions by gas chromatography. Pentane of 0.2 pmol/mg protein/min was formed in the presence of NADPH without CCl4. Pentane formation increased to 2.0 pmol/mg protein/min in the presence of CCl4 and NADPH. ...

Nicotinic acid phosphoribosyltransferase (EC 2.4.2.11) (NaPRTase) is the rate-limiting enzyme in the three-step Preiss-Handler pathway for the biosynthesis of NAD. The enzyme catalyzes the conversion of nicotinic acid (Na) and 5-phosphoribosyl-1-pyrophosphate (PRPP) to nicotinic acid mononucleotide (NaMN) and pyrophosphate (PPi). Several studies have underlined the importance of NaPRTase for NA...

The activities of enzymes involved in the formation and catabolism of 6-thiopurine nucleotide were assayed in leukocytes of leukemic patients considered either suscepti ble or resistant to the 6-thiopurines. Altered ratios of the activities of hypoxanthine-guanine phosphoribosyltransferase (H-GPRT) and adenine phosphoribosyltransferase were noted in leukocytes from 3 of 11 resistant acute nonly...

The isolation and characterization of stable mouse Tlymphoma (549) cell variants which have altered levels of both orotate phosphoribosyltransferase and orotidylate decarboxylase are reported. These clones were selected for resistance to either 6-azauridine or S-fluorouracil, two toxic pyrimidine analogs. The cells of one clone, AU-11, are lo-fold more resistant to 6-azauridine than wild type 5...

Some of the factors responsible for the control of pyrimidine nucleotide biosynthesis in intact cells have been investigated using rat hepatoma cells grown in continuous culture. The addition of uridine (0.5 mM) to culture medium causes a decrease of approximately 70% in the rate of de nouo pyrimidine nucleotide biosynthesis, as determined by incorporation of WO 2. Maximum inhibition of W02 inc...

Hypoxanthine phosphoribosyltransferase (inosine monophosphate: pyrophosphate phosphoribosyltransferase EC 2.4.2.8) has been purified SO-fold from an acid-treated lysate of human erythrocytes. The average particle weight of the enzyme was estimated by gel filtration at 60,000. Between the pH values of 7.1 and 9.1 no marked difference in the initial velocity of IMP synthesis was observed. Kinetic...

The word sepsis was derived from the Greek word: sêpsis, which means the state of putrefaction or decay. Sepsis is a potentially deadly medical condition that is characterized by a whole-body inflammatory state, called a systemic inflammatory response syndrome, and the presence of a known or suspected infection. The more critical subsets of sepsis are severe sepsis with acute organ dysfunction,...

Key-words Disease name and synonyms Definition Excluded diseases Diagnosis criteria Differential diagnosis Prevalence Molecular defect Clinical description Management including treatment Etiology Diagnostic methods Antenatal diagnosis Unresolved questions References Abstract Adenine phosphoribosyltransferase (APRT) catalyzes the synthesis of AMP (adenosine monophosphate) from adenine and 5'-pho...

The mechanism of reaction of human erythrocyte hypoxanthine-guanine phosphoribosyltransferase was investigated by initial velocity, product inhibition, and isotope exchange studies. Although initial velocity data are compatible with a mechanism involving binary enzyme-substrate complexes, the product inhibition and isotope exchange studies indicate that the reaction is ordered with the formatio...

Human adenine phosphoribosyltransferase has been purified 33,000-fold from erythrocytes to a specific activity of 9.58 pmoles of AMP formed per mg of protein per min. The native enzyme has a molecular weight of 34,000 and is composed of three subunits of equal molecular weight which appear to be associated by noncovalent forces. The highly purified enzyme is maximally active over a broad pH ran...