Photoaffinity cross-linking of F1ATPase from spinach chloroplasts by 3''-arylazido-β-alanyl-8-azido ATP

UV irradiation of the ATPase (CF₁) from spinach chloroplasts in the presence of 3'-arylazido-β-alanyl-8-azido ATP (8,3'-DiN₃ATP) results in a nucleotide-dependent inactivation of the enzyme and in a nucleotide-dependent formation of -β cross-links. The results demonstrate an interfacial localization of the nucleotide binding sites on CF₁.     

α2-Adrenoceptor-Mediated Inhibition of Electrically Evoked [3H]Noradrenaline Release from Chick Sympathetic Neurons: Role of Cyclic AMP

Abstract: This study explores the role of cyclic AMP in electrically evoked [³H]noradrenaline release and in the α₂-adrenergic modulation of this release in chick sympathetic neurons. Along with an increase in stimulation-evoked tritium overflow, applications of forskolin enhanced the formation of intracellular cyclic AMP. Both effects of forskolin were potentiated by the phosphodiesterase inhibitor 3-isobutyl-1-methylxanthine. The forskolin-induced increase in overflow was abolished by the Rp-diastereomer of cyclic AMP-thioate, an antagonist at cyclic AMP-dependent protein kinases, and 1,9-dideoxy-forskolin, an inactive analogue at adenylyl cyclase, had no effect on the evoked overflow. A 24-h pretreatment with either cholera toxin or forskolin reduced the subsequent forskolin-induced accumulation of cyclic AMP and inhibited the stimulation-evoked release. Basal cyclic AMP production, however, remained unaltered after forskolin treatment and was enhanced after 24 h of cholera toxin exposure. The α₂-adrenergic agonist bromoxidine did not affect the formation of cyclic AMP stimulated by forskolin but reduced electrically evoked release. However, effects of bromoxidine on ³H overflow were attenuated by forskolin as well as by 8-bromo-cyclic AMP. Effects of bromoxidine on [³H]noradrenaline release were paralleled by an inhibition of voltage-activated Ca²⁺ currents, primarily through a delayed time course of current activation. This effect was abolished when either forskolin or 8-bromo-cyclic AMP was included in the pipette solution. Both substances, however, failed to affect Ca²⁺ currents in the absence of bromoxidine. These results suggest that the signaling cascade of the α₂-adrenergic inhibition of noradrenaline release involves voltage-activated Ca²⁺ channels but not cyclic AMP. Elevated levels of cyclic AMP, however, antagonize this α₂-adrenergic reduction, apparently through a disinhibition of Ca²⁺ channels.     

A neural network model for the prediction of membrane-spanning amino acid sequences

The architecture and weights of an artificial neural network model that predicts putative transmembrane sequences have been developed and optimized by the algorithm of structure evolution. The resulting filter is able to classify membrane/nonmembrane transition regions in sequences of integral human membrane proteins with high accuracy. Similar results have been obtained for both training and test set data, indicating that the network has focused on general features of transmembrane sequences rather than specializing on the training data. Seven physicochemical amino acid properties have been used for sequence encoding. The predictions are compared to hydrophobicity plots.     

Polyamine Metabolism in Experimental Brain Tumors of Rat

Abstract: Biosynthesis and accumulation of the polyamines putrescine, spermidine, and spermine are closely associated with cellular growth processes. We examined polyamine levels and the activity of their first rate-limiting enzyme, ornithine decarboxylase (ODC), in stereotactically induced experimental gliomas of the rat brain 1 and 2 weeks after implantation. Regional ODC activity and polyamine levels were determined in the tumor and in the ipsi- and contralateral striatum, white matter, and cerebral cortex. In the tumor, both ODC activity and polyamine levels markedly increased with progressive tumor growth, as compared to those in the white matter of the opposite hemisphere. In the peritumoral brain tissue, ODC activity did not change, but there was a marked increase of putrescine and, to a lesser degree, of spermidine and spermine almost throughout the whole ipsilateral hemisphere. ODC activity, therefore, seems to be a reliable marker of neoplastic growth in the brain, which may be of use for new clinical concepts of the diagnosis and therapy of brain tumors. The more diffuse distribution of polyamines, however, may be associated with the formation and spreading of edema, which would explain some of the biological effects of tumors on distant brain tissue.     

Methyl chloride metabolism of the strictly anaerobic,methyl chloride-utilizing homoacetogen strain MC

The methyl chloride metabolism of the homoacetogenic, methyl chloride-utilizing strain MC was investigated with cell extracts and cell suspensions of the organism. Cell extracts were found to contain all enzyme activities required for the conversion of methyl chloride or of H₂ plus CO₂ to acetate. They catalyzed the dechlorination of methyl chloride with tetrahydrofolate as the methyl acceptor at a rate of 20 nmol/min × mg of cell protein. Also, the O-demethylation of vanillate with tetrahydrofolate could be measured at a rate of 40 nmol/min × mg. Different enzyme systems appeared to be responsible for the dehalogenation of CH₃Cl and for the O-demethylation of methoxylated aromatic compounds, since cells grown with methoxylated aromatic compounds exhibited a significantly lower activity of CH₃Cl conversion than methyl chloride grown cells and vice versa. In addition, ammonium thiocyanate (5 mM) completely inhibited CH₃Cl dechlorination, whereas the consumption of vanillate was not affected significantly. The data were taken to indicate, that the methyl chloride dehalogenation is catalyzed by a specific, inducible enzyme present in strain MC, and that tetrahydrofolate rather than the corrinoid-protein involved in acetate formation is the primary acceptor of the methyl group in the dechlorination reaction.     

The use of the nonradioactive digoxigenin chemiluminescent technology for plant genomic Southern blot hybridization: A comparison with radioactivity

A nonradioactive labelling and detection method for plant genomic DNA analysis is compared to the radioactive method. The radioisotopes are replaced by a nucleotide, digoxigenin-11-dUTP, and the signal detection is accomplished by the enzymatic reaction of alkaline phosphatase, conjugated to anti-digoxigenin antibodies, with the chemiluminescent substrate AMPPD (3-(2-spiroadamantane)-4-methoxy-4(3 phosphorytoxy) phenyl-1, 2-dioxetane). The sensitivity of the radioactive and nonradioactive methods are directly compared using identical Southern blots subjected to the radioactive and nonradioactive detection. The advantages of this nonradioactive method are discussed.     

Stereoselective HPLC bioanalysis of atenolol enantiomers in plasma: Application to a comparative human pharmacokinetic study

An enantioselective HPLC bioassay has been developed relying on extraction of (R)- and (S)-atenolol from alkalinized plasma or serum (pH > 12) into dichloromethane containing 5% (v/v) 1-butanol followed by an achiral derivatization of the drug with phosgene leading to (R)- and (S)-oxazolidine-2-one derivatives. Under these conditions there was quantitative conversion of the acetamido group to the corresponding nitrile. These stable derivatives were separated on a (R,R)-diaminocylohexane-dinitrobenzoyl chiral stationary phase [(R,R)-DACH-DNB] using dichloromethane/methanol 98/2 as mobile phase. Determination limits of 0.5 ng for (R)- and 0.6 ng for (S)-atenolol could be achieved using fluorimetric detection. The assay was applied to a human pharmacokinetic study which was performed in a randomized cross-over, double-blind fashion in 12 healthy volunteers, administering single oral doses of 100 mg (R,S)-, 50 mg (R)-, and 50 mg (S)-atenolol AUC_0–24 and C_max values of (R)-atenolol were slightly but significant higher than those of (S)-atenolol. The R/S ratios were 1.09 for AUC(R)/AUC(S) and 1.03 for C_max (R)/C_max(S) (P < 0.01) respectively after administration of the racemic drug. However, there were no differences between AUC, C_max, and t_½ values of each enantiomer, whether they were administered as single enantiometers or in the form of its racemic mixture. © 1993 Wiley-Liss, Inc.