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Biomedical subjects

G Weber

Publications and source records attributed to G Weber.

At least 649 records · Page 36Linked to original sources
PubMed1978

Improved radioisotopic assay for cytidine 5'-triphosphate synthetase (EC 6.3.4.2).

An improved radioassay for cytidine 5-triphosphate synthetase is reported which employs thin-layer chromatographic methods and provides a number of advantages over previously available techniques. (i) The method resolves the nucleotides and the degradation products generated during the time course of the enzymatic reaction by ascending chromatography employing polyethyleneimine cellulose plastic-backed sheets. (ii) Determinations of CTP formed and all nucleotide pairs generated during kinetic analysis of CTP synthetase are greatly simplified, further facilitating the detection of extraneous enzymatic activities. (iii) The sensitivity of the assay is enhanced and as little as 50 pmol of product formed was readily detected in supernatant fluids. This was made possible, in part, by the addition of NaF and phosphoenolpyruvate which together maintain the nucleotide triphosphates in the reaction mixture. (iv) A large number of samples can be handled at one time with highly reproducible results. The synthesis of CTP from UTP by enzyme preparations from rat liver, hepatomas, and Salmonella typhimurium LT2 was quantitated with this method.

Animals↗
PubMed1978

Facial duplication -- the unique case of Antonio.

A case of facial duplication with its surgical correction in childhood and the consequences on facial growth is reported. It is a unique case in the duration of observation. The following structures were fully duplicated: the nose, the premaxilla, the cribriform plate, the crista galli. In addition there was an enormous facial cleft including lip, alveolus and palate. Additionally there were two rudimentary eye sockets, eyes, and two supplementary eyebrows. The monstrous hypertelorism with the facial duplication was corrected at the age of ten. The surgical procedure is described and the postoperative complications are discussed. Gross lack of growth of the middle third of the facial skeleton was observed. This was probably the consequence of the initial corrective surgery. Overgrowth of the mandible created a gorilla-like appearance by the end of the growth period. This was corrected in one operation by advancement of the middle third in three sections and repositioning of the mandible as a whole together with the mandibular anterior alveolar segment. Finally all parts of the lower half of the nose had to be enlarged, both soft tissues as well as the cartilaginous framework. A pharyngoplasty in addition to the correction of the intermaxillary abnormalities did much to improve the speech quality of the patient. A large secondary cranial defect was successfully reconstructed with the use of 14 halved ribs. In spite of the removal of four ribs from one side and three ribs from the other, there were no postoperative respiratory problems. Spontaneous rib regeneration was found where ribs had been removed one year earlier.

Adolescent↗
PubMed1978

Adenosine deaminase and adenosine kinase in rat hepatomas and kidney tumours.

Adenosine deaminase and adenosine kinase have been measured in rat liver, 12 transplantable hepatomas, regenerating, foetal and neonatal liver, adult and neonatal rat kidney and 2 transplantable kidney tumours. Adenosine, deaminase activity, relative to the normal liver value, was elevated 2-4 fold in hepatomas of rapid growth rate, was in the normal range in more slowly growing hepatomas and in regernerating liver, and was low in foetal and neonatal liver. Adenosine kinase activity was decreased, relative to rat liver values, in all the hepatomas; activity of this enzyme gave a negative correlation with tumour growth rate. Kinetic properties of the two enzymes were examined in partially purified preparations. Adenosine deaminases from both liver and rapidly growing hepatoma 3924A were subject to weak product inhibition by inosine. Adenosine kinase from liver and hepatoma 3924A was inhibited by the reaction products ADP and AMP, and the enzyme was also subject to excess substrate inhibition by concentrations of ATP in excess of 1 mM. In rat hepatoma cell lines growing in culture, the toxicity of adenosine correlated inversely with the ratio of adenosine deaminase activity to adenosine kinase activity. Chromatographic measurements showed that hepatoma cells incorporated less extracellular adenosine into their adenine nucleotide pools than did isolated liver cells. These results indicate that increased adenosine deaminase activity and decreased adenosine kinase activity may confer a selective advantage upon the cancer cell.

Adenosine↗
PubMed1978

Ligand-promoted transfer of proteins between phases: spontaneous and electrically helped.

A model system for the partitioning of peripheral membrane proteins into membranes by ligand binding has been examined experimentally. Both bovine serum albumin and lysozyme partition between water and 1-butanol by the addition of sodium p-toluene sulfonate at pH 2.4. The partitioning is characterized by high orders of reaction: 25 and 10, respectively. Theory indicates that these high orders of reaction need not result from cooperative ligand binding in either phase, but depend primarily upon the number N of protein sites at which the transfer-promoting ligant binds, and on the difference in free energy of formation delta F0s of the protein--ligand complexes in the two phases. From the reaction orders and the experimental values of N, 80 for albumin and 11 for lysozyme, delta F0s was calculated to be --0.5 kcal/mol (--2.1 kJ/mol) and --0.8 kcal/mol (--2.5 kJ/mol) per ligand bound, respectively. Experiments measuring the dependence on ligand concentration of the rate of protein electrophoresis across the water/butanol interface are described. These rates increase by more than two orders of magnitude as the ligand concentration approaches the critical value for partition and are inversely dependent on the number of ligant sites for the two proteins studied.

Ligands↗
PubMed1977

Effect of pressure upon the fluorescence of various flavodoxins.

The effects of hydrostatic pressure in the range of 10(-3) to 11 kbar on the fluorescence of flavodoxins from Peptostreptococcus elsdenii, Desulfovibrio vulgaris, Azotobacter vinelandii, and Clostridium MP were investigated. The first three flavoproteins showed under high pressure enhancements of flavin fluorescence of over 50 times resulting from the release of flavin mononucleotide from the protein complex. The Clostridial flavodoxin showed a very much smaller fluorescence change. At pH 7.5 the high-pressure fluorescence changes of the flavodoxins of D. vulgaris and P. elsdenii were not reversed by decompression, but in A. Vinelandii the pressure changes were over 80% reversible. At pH 5 over 80% reversibility was restored to the flavodoxins of D. vulgaris and P. elsdenii, although the pressure dependence of the fluorescence changes was very similar in the reversible and irreversible cases. The midpoint pressures in the reversible reactions were 4.7 kbar (D. vulgaris), 8.7 kbar (P. elsdenii), and 10.6 kbar (A. vinelandii) indicating specific differences in the flavin binding regions. Apparent volume changes in these reactions were 65-75 mL/mol indicating participation of a large fraction of the protein in the pressure-induced changes. The irreversible changes are not related to protein aggregation and are believed to result from a pressure-dependent covalent modification, not yet characterized, of the flavin binding region of the protein.

Azotobacter↗
PubMed1977

Volume changes in the formation of internal complexes of flavinyltryptophan peptides.

The effect of pressure, up to 10 kbar, on the fluorescence yield and lifetime of two flavinyltryptophan peptides was investigated. These peptides differed only in the number of methylene groups, respectively three and five, separating the chromophores. At atmospheric pressure the closed nonfluorescent form predominated in both compounds constitutin 94% of the total in the short-linked peptide and 80% in the long-linked one. The fluorescence of both peptides decreased at high pressure and the volume change upon formation of the nonfluorescent complex in the short peptide (--1.8 mL/mol) was less than half of the change in the long peptide (--4.8 mL/mol) or the value for FAD (--4.3 mL/mol). The much smaller compressibility of the short peptides is attributed to the mechanical constraint to the approach of the interacting rings, imposed by the short link. Mechanical constraints of similar nature may be expected to be operative in proteins. Their importance in pressure denaturation is discussed.

Flavoproteins↗
PubMed1977

Partial purification, properties and regulation of inosine 5'phosphate dehydrogenase in normal and malignant rat tissues.

IMP dehydrogenase (EC 1.2.1.14) was purified 180-fold from rat liver and from the transplantable rat hepatoma 3924A. The enzymes from the two sources were apparently identical; they exhibited hyperbolic saturation kinetics and an ordered, sequential mechanism, and were subject to inhibition by a number of purine nucleotides. Km values for the substrates, IMP and NAD+, were 12 and 24 micrometer respectively. IMP dehydrogenase activity in a spectrum of rat hepatomas was increased, relative to normal liver, by 2.5--13-fold; these increases correlated with tumour growth rate. Activity in two rat kidney tumours was increased 3-fold relative to that in normal renal cortex; control of activity of this enzyme is apparently altered in neoplastic cells. After partial hepatectomy, IMP dehydrogenase activity began to rise 6 h after operation, reaching a peak of 580% of normal activity by 18 h. Activity in neonatal liver, however, was only slightly higher than that in the adult. Organ-distribution studies showed highest enzyme activities in spleen and thymus. In livers of rats starved for 3 days, where all enzymes, except those involved in gluconeogenesis, showed decreased activity IMP dehydrogenase activity was increased; this change was accompanied by a rise in hepatic GTP concentrations. It is concluded that IMP dehydrogenase is a key enzyme in the regulation of GTP production, and thus involved in regulation of nucleic acid biosynthesis. The increased activity of IMP dehydrogenase in liver of starved rats may be related to the requirements for GTP for gluconeogenesis.

Animals↗
PubMed1977

Aortic surface coat scanning electron-microscopic modifications after short-term hypercholesterolic diet, visualized in rabbits by con A-haemocyanin reaction.

Modifications of the aortic endothelial surface coat have been visualized at SEM with the use of the Con A-haemocyanin method. After fifteen days of an atherogenic diet, a strong increase of the reactive coat was evident in areas near the orifice of the collateral branches. In other areas, the reaction appeared to be intensely diminished.

Animals↗