Effect of propionate and pyruvate on citrulline synthesis and ATP content in rat liver mitochondria.

Propionate inhibits citrullinogenesis when succinate (plus rotenone) or glutamate are the oxidizable substrates used. Propionate decreases the intramitochondrial concentration of carbamylphosphate by decreasing the ATP content. When the energy supply for citrullinogenesis is provided by an influx of exogenous ATP, propionate is no longer an inhibitor. Pyruvate inhibits citrullinogenesis with glutamate but not with succinate (plus rotenone) as oxidizable substrates. Propionate and pyruvate deplete mitochondrial ATP but probably by different mechanisms.     

Studies on the regeneration-restore and karyotype of protoplast in Metarhizium anisopliae var. majus

Abstract:  The characteristics and regeneration-restore of protoplasts and its karyotype of an insect pathological fungus, Metarhizium anisopliae var. majus were studied. Among the protoplasts, 25.3% were without a nucleus, and 74.7% contained a nucleus. Among the nucleus protoplasts, 53.6% contained a single nucleus. The regeneration-restore of protoplasts was of three distinct shapes. Considering the frequency of regeneration and the growing speed of the colony, 0.7 mol/l glucose was the optimum as osmotic stabilizer of culture medium in the regeneration-restore of the protoplasts. The chromosomal DNA molecules of M. anisopliae var. majus have been separated into seven bands by pulsed-field gel electrophoreses. Using the Schizosaccharomyces pombe chromosomes as size standard, the size of chromosomal DNA was estimated to be 1.1–6.5 Mb and its karyotype exhibited polytypism among strains.     

Active compounds in Populus nigra L. wilted leaves responsible for attracting Helicoverpa armigera (Hübner) (Lep., Noctuidae) and new agaropectin formulation

Abstract:  The leaf extracts of Populus nigra were collected and identified by steam distillation, air entrainment and gas chromatographic–mass spectrometric analysis. Electroantennograms were recorded from Helicoverpa armigera adults in response to the chemicals identified. Both aromatic compounds and green-leaf volatiles elicited strong responses. Field experiments revealed that the active compounds responsible for attracting H. armigera moths are mainly short-side-chain aromatic alcohols and aldehydes. We, for the first time, used agaropectin as the controlled-release matrix of insect attractants. A five-component lure containing all the aromatics without phenolics, mixed in the proportions as found in the steam distillate of the leaves collected in August, produced the best trap catch. The results showed that the volatiles of wilted leaves of P. nigra can attract H. armigera adults by feeding attraction.     

Voltage-dependent depolarization of bacterial membranes and artificial lipid bilayers by the peptide antibiotic nisin

The peptide antibiotic nisin is shown to disrupt valinomycin-induced potassium diffusion potentials imposed on intact cells of Staphylococcus cohnii 22. Membrane depolarization occurred rapidly at high diffusion potentials while at low potentials nisin-induced depolarization was slower suggesting that nisin requires a membrane potential for activity. This assumption was proven in experiments with planar lipid bilayers (black lipid membranes). Macroscopic conductivity measurements indicated a voltage-dependent action of nisin. The potential must have a trans-negative orientation with respect to the addition of nisin (added to the cis-side) and a sufficient magnitude (ca. -100 mV). With intact cells the threshold potential was lower (-50 to -80 mV at pH 7.5 and below -50 mV at pH 5.5). Single channel recordings resolved transient multistate pores, strongly resembling those introduced by melittin into artificial bilayers. The pores had diameters in the range of 0.2–1 nm, and lifetimes of few to several hundred milliseconds. The results indicate that nisin has to be regarded as a membrane-depolarizing agent which acts in a voltage-dependent fashion.Abbreviations BLM Black lipid membranes - CCCP carbonyl cyanide m-chlorophenylhydrazone - DOPC dioleoyl phosphatidylcholine - PS phosphatidylserine - TPP⁺ tetraphenylphosphonium cation     

Antimutagenic effect of garlic (Allium sativum L.) on 4NQO-induced mutagenesis in Escherichia coli WP2

Aqueous extract prepared from garlic bulbs markedly suppressed the mutagenesis in both E. coli WP2 trp- and E. coli WP2 trp- uvrA- induced by 4-nitroquinoline 1-oxide (4NQO), but not that induced by UV. Cellular toxicity, inhibition of the expression of the Trp+ phenotype and delay of the first cell division after 4NQO treatment were not observed in the presence of the extract. Since the extract showed identical antimutagenic effects against 4NQO in both test strains but no effect on the mutagenesis of UV, it seems that the extract might act by inactivating the electrophilic group(s) of 4NQO or inhibiting its metabolic activation.     

Insulin-stimulated alpha-(methyl)aminoisobutyric acid uptake in skeletal muscle. Evidence for a short-term activation of uptake independent of Na+ electrochemical gradient and protein synthesis.

1. The present study was designed to explore the mechanisms by which insulin stimulates system A of amino acid transport in extensor digitorum longus (EDL) muscles, by using a system A analogue, alpha-(methyl)aminoisobutyric acid (MeAIB). 2. Insulin stimulation of MeAIB uptake was noted after only 30 min of incubation and was maximal at 60 min. Kinetics of the insulin effect on MeAIB uptake were characterized by an increased Vmax. without modification of Km for MeAIB. 3. Incubation of EDL muscles with cycloheximide for 90 min did not modify MeAIB uptake in either the presence or the absence of insulin, indicating the independence of insulin action from protein synthesis de novo. Incubations for 180 min with cycloheximide caused a decrease in basal MeAIB uptake; however, the percentage stimulation of amino acid transport by insulin was unaltered. Basal MeAIB uptake was increased by incubation for 180 min, but under these conditions no change in the percentage effect of insulin was found. 4. Ouabain, gramicidin D, or both, markedly decreased basal MeAIB uptake by EDL muscle, but the percentage effect of insulin was unaltered. 5. We conclude that insulin action on amino acid transport through system A in muscle is rapid, is characterized by an increased Vmax., and is independent of protein synthesis de novo and the Na+ electrochemical gradient. Our data are compatible with insulin acting directly on the system A transporter.