Stimulation by the phosphodiesterase inhibitor 3-isobutyl-1-methylxanthine of rat hepatic polyamine biosynthesis in vivo

Intraperitoneal injection of the phosphodiesterase inhibitor, 3-isobutyl-1-methylxanthine (IBMX), resulted in a rapid and transient induction of rat hepatic ornithine decarboxylase (ODC) activity. Maximal activity was found about 5 hr after application. The levels of putrescine and spermidine increased accordingly, reaching a maximum at 7 and 12 hr following injection, respectively, while the concentration of spermine remained almost constant. The implications of these findings are discussed in relation to the mechanism of induction of ornithine decarboxylase and concomitant polyamine biosynthesis.     

Induction by folate and folate analogs of extracellular and membrane-bound phosphodiesterase from Dictyostelium discoideum

Folate stimulation is known to enhance Dictyostelium discoideum differentiation. During early differentiation, D. discoideum cells possess two classes of folate receptors which can be distinguished by their difference in specificity (R. J. W. de Wit, FEBS Lett. 150, 445-448, 1982). We investigated the type of receptor by which folate affects cell differentiation. Two independently regulated developmental markers were used: the extracellular phosphodiesterase-inhibitor system and cell-surface phosphodiesterase activity. Our results indicate that the major effect of folate on development is mediated by the folate-specific receptor. The nonspecific folate receptor was only involved in a minor, transient enhancement of the extracellular phosphodiesterase activity very early in development.     

Collaborative study on the isolation of salmonella from artificially contaminated milk powder

The suitability of artificially contaminated milk powder as a substrate for salmonella reference samples and its stability under different storage conditions were studied. The need for a reconstitution step in the standard isolation method for salmonellas from milk powders was also investigated. When milk powder was examined in this way with a reconstitution step, differences in laboratory methods and/or storage times had no significant effect on the results after storage at 4 degrees C. With powder stored at room temperature there was a systematic decrease in the number of samples positive as the storage time increased. It is concluded therefore that milk powder contaminated with salmonellas should be stored at 4 degrees C. Examination of such milk powder with a reconstitution step yielded better results than without it and this step is therefore necessary for improving the reproducibility of the method. No significant differences were encountered between the standard isolation method and that used in the authors' laboratories. The results of this study indicate that milk powder is suitable as basic material for reference samples and that a reconstitution step should be included in the standard salmonella isolation procedure.     

Energy transduction by electron transfer via a pyrrolo-quinoline quinone-dependent glucose dehydrogenase in Escherichia coli, Pseudomonas aeruginosa, and Acinetobacter calcoaceticus (var. lwoffi).

The coupling of membrane-bound glucose dehydrogenase (EC 1.1.99.17) to the respiratory chain has been studied in whole cells, cell-free extracts, and membrane vesicles of gram-negative bacteria. Several Escherichia coli strains synthesized glucose dehydrogenase apoenzyme which could be activated by the prosthetic group pyrrolo-quinoline quinone. The synthesis of the glucose dehydrogenase apoenzyme was independent of the presence of glucose in the growth medium. Membrane vesicles of E. coli, grown on glucose or succinate, oxidized glucose to gluconate in the presence of pyrrolo-quinoline quinone. This oxidation led to the generation of a proton motive force which supplied the driving force for uptake of lactose, alanine, and glutamate. Reconstitution of glucose dehydrogenase with limiting amounts of pyrrolo-quinoline quinone allowed manipulation of the rate of electron transfer in membrane vesicles and whole cells. At saturating levels of pyrrolo-quinoline quinone, glucose was the most effective electron donor in E. coli, and glucose oxidation supported secondary transport at even higher rates than oxidation of reduced phenazine methosulfate. Apoenzyme of pyrrolo-quinoline quinone-dependent glucose dehydrogenases with similar properties as the E. coli enzyme were found in Acinetobacter calcoaceticus (var. lwoffi) grown aerobically on acetate and in Pseudomonas aeruginosa grown anaerobically on glucose and nitrate.     

Use of fluorinated tyrosine phosphates to probe the substrate specificity of the low molecular weight phosphatase activity of calcineurin

Calcineurin, a calmodulin-activated protein phosphatase, is known to dephosphorylate certain low molecular weight phosphate esters. The low molecular weight phosphatase activity of calcineurin has been studied by utilizing tyrosine phosphate derivatives. Kinetic studies suggest that the substrate specificity is dependent upon the electronic nature of the substrate in contrast to results obtained with alkaline phosphatase from Escherichia coli. Comparison of calcineurin and acid-catalyzed hydrolyses indicates a 1:1 correlation between the rate constants for the two processes. This correlation and other model studies have been utilized to provide insight into the chemical mechanism of calcineurin. Possible chemical mechanisms for calcineurin are discussed.     

Purification and properties of a prothrombin activator from the venom of Notechis scutatus scutatus

The prothrombin activator present in the venom of the mainland tiger snake (Notechis scutatus scutatus) was purified to homogeneity by gel chromatography on Sephadex G-200 followed by ion-exchange chromatography on SP-Sephadex. The venom activator has an apparent molecular weight of 54,000. It consists of a heavy chain (Mr = 32,000) and a light chain (Mr = 23,000) held together by one or more disulfide bridges. The active site is located at the heavy chain region of the molecule. The venom activator contains 8 gamma-carboxyglutamic acid residues/molecule. Gel electrophoretic analysis of prothrombin activation indicates that the venom activator is capable of cleaving both the Arg 274-Thr 275 and Arg 323-Ile 324 bonds of bovine prothrombin. The order of bond cleavage appears to be random since prethrombin-2 and meizothrombin occur as intermediates during prothrombin activation. Prothrombin activation by the venom activator alone is very slow. This is explained by the unfavorable kinetic parameters for the reaction (Km for prothrombin = 105 microM, Vmax = 0.0025 nmol of prothrombin activated per min/microgram of venom activator). Phospholipids plus Ca2+ and Factor Va greatly stimulate venom-catalyzed prothrombin activation. In the presence of 50 microM phospholipid vesicles composed of 20 mol % phosphatidylserine and 80 mol % phosphatidylcholine, the Km drops to 0.2 microM, whereas there is hardly any effect on the Vmax. Factor Va causes a 3,500-fold increase of the Vmax (8.35 nmol of prothrombin activated per min/microgram of venom activator) and a 10-fold decrease of the Km (9.5 microM). The most favorable kinetic parameters are observed in the presence of both 50 microM phospholipid and Factor Va (Km = 0.16 microM, Vmax = 27.9 nmol of prothrombin activated per min/microgram of venom activator). These changes of the kinetic parameters explain the stimulatory effects of Factor Va and phospholipid on venom-catalyzed prothrombin activation. The venom activator slowly converts the Factor Xa-specific chromogenic substrates CH3SO2-D-leucyl-glycyl-L-arginine-p-nitroanilide and N-benzoyl-L-isoleucyl-L-glutamyl-(piperidyl)-glycyl-L-arginyl-p-nitroani lide hydrochloride. Factor Va causes a 7-fold stimulation of chromogenic substrate conversion by the venom activator. This stimulation appears to be the result of the formation of a tight 1:1 complex between the venom activator and Factor Va.     

Purification and partial characterization of the b-type cytochrome from human polymorphonuclear leukocytes

Polymorphonuclear leukocytes contain an oxidase system that can be activated to produce superoxide radicals and hydrogen peroxide. A nonmitochondrial b cytochrome, functioning in the generation of these oxygen species, has been purified to apparent homogeneity from human polymorphonuclear phagocytes. After solubilization of the cytochrome with Triton X-100, the cell extract was subsequently chromatographed on Blue Sepharose and Sephacryl S-300. The final preparation was maximally purified 170-fold with a specific content of 5.33 +/- 2.03 nmol mg-1 of protein (mean +/- S.D.; n = 7) and a yield of 21 +/- 13% (n = 5). The apparent molecular mass of the nondenatured cytochrome was estimated by gel filtration to be 235 kDa. Upon polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate, a single polypeptide was found with a molecular mass of 127 kDa. From the pyridine hemochrome spectrum 1 protoheme IX/polypeptide was calculated. The light absorbance bands of the dithionite-reduced cytochrome were found to be at 558.5 (alpha), 529 (beta), and 426 nm (Soret), and that of the oxidized cytochrome at 413.5 nm. The difference absorbance coefficients are delta epsilon (426.5 - 440 nm) = 160.6 +/- 11 mM-1 cm-1 and delta epsilon (558.5 - 542 nm) = 29.3 +/- 2 mM-1 cm-1 (mean +/- S.D.; n = 5). Carbon monoxide binds to the cytochrome in a time-dependent fashion (maximum binding after 50-60 min). The midpoint potential of the solubilized nonpurified cytochrome is identical to the cytochrome in situ (Em7.0 = -218 +/- 7 mV (mean +/- S.D.; n = 5)). However, purified cytochrome b shows a significantly decreased midpoint potential, estimated at -407 +/- 18 mV (n = 4). The protein does not contain noncovalently bound FAD or FMN, and no spectral evidence was obtained for the presence of covalently bound flavin. Preliminary amino acid analysis of the cytochrome shows a high content of hydrophilic residues.     

The influence of dolichol, dolichol esters, and dolichyl phosphate on phospholipid polymorphism and fluidity in model membranes

The effect of dolichols, polyprenols, dolichol esterified with fatty acids, and dolichyl phosphate on the structure and fluidity of model membranes was studied using 31P NMR, small-angle x-ray scattering, differential scanning calorimetry, and freeze-fracture electron microscopy. These studies suggest that dolichol and dolichol derivatives destabilize unsaturated phosphatidylethanolamine containing bilayer structures and promote hexagonal II phase formation; high concentrations of dolichol induce lipid structures characterized by "isotropic" 31P NMR and particulate fracture faces; dolichol, contrary to cholesterol, has no effect on the thermotropic behavior of membranes consisting of phosphatidylcholine, while dolichyl-P incorporation abolishes the transition from the gel to liquid crystalline phase in 1,2-dimyristoyl-sn-glycero-3-phosphocholine; both dolichol and dolichyl-P increase the fatty acid fluidity in phosphatidylethanolamine mixtures; the effect of dolichol on bilayer structure and fluidity is more pronounced with increasing number of isoprene residues; dolichol esters are only soluble to a limited extent in the bilayer and segregates into domains at low concentrations; the results are consistent with a localization of dolichyl-P in which the phosphate group is oriented to the water interphase. The induction of hexagonal II phase by dolichyl-P may elicit the transmembrane movement of glycosylated lipid intermediate.