ACTH-induced inhibition of endogenous rat brain protein phosphorylation in vitro: Structure activity

ACTH_1–24 inhibits the endogenous phosphorylation in vitro of distinct SPM protein bands. Using N-terminal fragments of ACTH, the structure-activity requirements for this effect were studied. A rather complex interaction of the ACTH fragments with endogenous SPM phosphorylation was observed. The effects were not only dependent on the primary structure of the peptide used, but also on the protein band studied and the ATP/SPM ratio used in the incubation system. ACTH_1–24 did not interfere with the ATP-hydrolyzing activity of the SPM preparation, nor did it influence the endogenous phosphatase activity. Therefore, a direct interaction of ACTH with SPM protein kinase(s) is likely to be responsible for its effect on phosphorylation.     

Ethylene-promoted formation of aerenchyma in seedling roots of Zea mays L. under aerated and non-aerated conditions

The role of ethylene in the formation of lysigenous cortical cavities (aerenchyma) in seedling roots of Zea mays L. cv. Capella, has been studied under aerated and non-aerated conditions. Passing roots from air to aerated water or from an aerated nutrient solution to a non-aerated solution, promoted cavity formation and was accompanied by an increase of the endogenous ethylene concentration. When the endogenous ethylene concentration of roots in aerated nutrient solutions, which otherwise would not produce much cavities, was enhanced by applying ethylene gas (0.1 and 1.0 μl 1^-1 in air) or the ethylene precursor 1-aminocyclopropane-1-car-boxylic acid, cavity formation was promoted. When, on the contrary, the endogenous ethylene concentration of the roots was reduced by adding the inhibitors of ethylene biosynthesis, cobalt ions and aminooxyacetic acid, or when the ethylene action was prevented by silver ions, cavity formation was prevented. It is concluded that endogenous ethylene controls the induction of cavity formation in the roots.     

Light-induced spectral changes of carotenoids in chromatophores of Rhodopseudomonas sphaeroides

Carotenoid difference spectra were recorded of chromatophores of Rhodopseudomonas sphaeroides energized with low light intensities versus chromatophores under dark conditions. The amplitudes of the peaks and troughs were dependent on the light intensities and the duration of illumination, but the shape of the difference spectra remained constant. Sharp isosbestic points were found at 515, 500, 481, 465, and 452 mm. When potassium-valinomycin-induced diffusion potentials (inside negative) were imposed on the chromatophores “mirror images” of the light-induced difference spectra were recorded with the same isosbestic points and the same positions but different relative amplitudes of the peaks and troughs. The results are explained in terms of changes in the shape of the vibrational splittings of the carotenoid main electronic transition. This could be the result of changes in the fluidity of the environment of the carotenoids upon energization of the membrane. Prolonged periods of illumination with low or high light intensities resulted in irreversible changes of the difference spectra. Short periods of illumination with high light intensities resulted in reversible elevations of the baseline and red shifts of peaks, troughs, and baseline crossings.     

The origin of mentha — gracilis (Lamiaceae). II. essential oils

Essential oils were eamined in nine clones of Mentha arvensis, four clones of M. spicata, and 20 clones of M. gracilis. An F₁ hybrid of M. arvensis M. spicata, selected on the basis of morphology and chromosome number, was matched with one clone of M. Gracilis. Genes for the inheritance of limonene, 1,8-cineole, linalool, isomenthone, carvone, and piperitenone oide were identified in one clone of M. arvensis and two clones of M. spicata. The range of essential oil compounds detected indicates that no one character can be used to identify M. gracilis, but the critical compounds of the oil of M. gracilis can be derived from crosses of M. arvensis M. spicata.     

NMR studies of lantibiotics. The structure of nisin in aqueous solution.

Nisin is a posttranslationally modified protein of 34 amino acids, and is a member of the class of bacteriocidal polypeptides known as lantibiotics, that contain the unusual amino acid lanthionine. Its structure in aqueous solution has been determined on the basis of NMR data, i.e. interproton distance constraints derived from nuclear Overhauser enhancement spectroscopy and torsion angle constraints derived from double-quantum-filtered correlated spectroscopy. Translation of the NMR constraints into a three-dimensional structure was carried out with the distance-geometry program DISMAN, followed by restrained energy minimization using CHARMm. The internal mobility of the peptide chain prohibited the determination of a precise overall folding of the molecule, but parts of the structure could be obtained, albeit sometimes with low resolution. The structure of nisin can best be defined as follows. The outermost N-terminal and C-terminal regions of nisin appear quite flexible, the remainder of the molecule consists of an amphiphilic N-terminal fragment (residues 3-19), joined by a flexible 'hinge' region to a rigid double-ring fragment formed by residues 23-28. The latter fragment has the appearance of a somewhat overwound alpha-helix. It is suggested, by assuming the presence of a (transient) alpha-helical structure in this part of prenisin, that the coupling between residues 23 and 26, as well as between 25 and 28, by thioether bridges, and the inversion of the C alpha chiralities at positions 23 and 25, can be rationalized.     

Malolactic fermentation: electrogenic malate uptake and malate/lactate antiport generate metabolic energy.

The mechanism of metabolic energy production by malolactic fermentation in Lactococcus lactis has been investigated. In the presence of L-malate, a proton motive force composed of a membrane potential and pH gradient is generated which has about the same magnitude as the proton motive force generated by the metabolism of a glycolytic substrate. Malolactic fermentation results in the synthesis of ATP which is inhibited by the ionophore nigericin and the F0F1-ATPase inhibitor N,N-dicyclohexylcarbodiimide. Since substrate-level phosphorylation does not occur during malolactic fermentation, the generation of metabolic energy must originate from the uptake of L-malate and/or excretion of L-lactate. The initiation of malolactic fermentation is stimulated by the presence of L-lactate intracellularly, suggesting that L-malate is exchanged for L-lactate. Direct evidence for heterologous L-malate/L-lactate (and homologous L-malate/L-malate) antiport has been obtained with membrane vesicles of an L. lactis mutant deficient in malolactic enzyme. In membrane vesicles fused with liposomes, L-malate efflux and L-malate/L-lactate antiport are stimulated by a membrane potential (inside negative), indicating that net negative charge is moved to the outside in the efflux and antiport reaction. In membrane vesicles fused with liposomes in which cytochrome c oxidase was incorporated as a proton motive force-generating mechanism, transport of L-malate can be driven by a pH gradient alone, i.e., in the absence of L-lactate as countersubstrate. A membrane potential (inside negative) inhibits uptake of L-malate, indicating that L-malate is transported an an electronegative monoanionic species (or dianionic species together with a proton). The experiments described suggest that the generation of metabolic energy during malolactic fermentation arises from electrogenic malate/lactate antiport and electrogenic malate uptake (in combination with outward diffusion of lactic acid), together with proton consumption as result of decarboxylation of L-malate. The net energy gain would be equivalent to one proton translocated form the inside to the outside per L-malate metabolized.     

Nucleotide sequence of the genome of the filamentous bacteriophage I2-2: Module evolution of the filamentous phage genome

Summary The nucleotide sequence of the circular single-stranded genome of the filamentous Escherichia coli phage I2-2 has been determined and compared with those of the filamentous E. coli phages Ff(M13, fl, or fd) and IKe. The I2-2 DNA sequence comprises 6744 nucleotides; 139 nucleotides less than that of the N- and I2-plasmid-specific phage IKe, and 337 (336) nucleotides more than that of the F-plasmid-specific phage Ff. Nucleotide sequence comparisons have indicated that I2-2, IKe, and Ff have a similar genetic organization, and that the genomes of I2-2 and IKe are evolutionarily more closely related than those of I2-2 and Ff. The studies have further demonstrated that the I2-2 genome is a composite replicon, composed of only two-thirds of the ancestral genome of IKe. Only a contiguous I2-2 DNA sequence of 4615 nucleotides encompassing not only the coat protein and phage assembly genes, but also the signal required for efficient phage morphogenesis, was found to be significantly homologous to sequences in the genomes of IKe and Ff. No homology was observed between the consecutive DNA sequence that contains the origins for viral and complementary strand replication and the replication genes. Although other explanations cannot be ruled out, our data strongly suggest that the ancestor filamentous phage genome of phages I2-2 and IKe has exchanged its replication module during evolution with that of another replicon, e.g., a plasmid that also replicates via the so-called rolling circle mechanism. Offprint requests to: R.N.H. Konings