Salicylate-promoted permeation of cefoxitin, insulin and phenylalanine across red cell membrane. Possible mechanism

Uptake of sodium cefoxitin, D-phenylalanine and insulin into human red blood cells was significantly enhanced by the presence of salicylate and 5-methoxysalicylate in the medium. The mechanism of adjuvant action appeared to depend on an affinity between the adjuvant and the protein fraction in the erythrocyte membrane. The inhibitory effect of DIDS and phlorizin on the salicylate-enhanced uptake of these compounds strongly suggests that the ability of salicylate to permeate the membrane may be essential for it to act as an adjuvant.     

Interactions of poly-N6-methyladenylic Acid and N6-substituted-9-methyladenines with poly-5-bromouridylic Acid: A Novel Base-pairing

Abstract

The interaction of poly-N⁶-methyladenylic acid (poly(m⁶A)) with poly-5-bromouridylic acid (poly(BU)) was studied by the mixing curve method. A 1 m⁶A: 2 BU stoichiometry was clearly indicated over a wide range of ionic strengths at neutral pH, while the binding of poly(m⁶A) to poly(U) is known to occur with 1 m⁶A:1 U. Digestion by nuclease S1 confirmed this stoichiometry, indicating the absence of single strands in a 1:2 mixture. Heating profile analysis and hydroxyapatite column chromatography provided further confirmation of this finding. To determine whether 1:2 stoichiometry holds in a monomer-polymer system, the interaction of N⁶-methyl-9-methyladenine (m⁶m⁹A), a corresponding monomer of poly(m⁶A), with poly(BU) was investigated.

Equilibrium dialysis experiments showed the stoichiometry of the interaction to be 1 m⁶A: 2 BU. Thus, we would describe some structural studies of the above complexes using c.d. and i. r. spectroscopy. Poly (m⁶A)·2poly(BU) and m⁶m⁹A·2poly(BU) are helical and analogous to each other in structure, and the bases in the complexes are all bound by hydrogen-bonding. N⁶-(Δ²-isopentenyl)- and N⁶-allyl-9-methyladenine were also found to form complexes with poly(BU), giving similar c.d. spectra with that of m⁶m⁹A·2poly(BU). The melting experiments indicated the T_ms to be substantially decreased, compared to the parent unmodified complexes, even though the T_m dependence of the polymer complex on salt concentration conforms to the typical triple strand. In the following, the biological significance of this novel pairing will be discussed.     

Effects of Exogenous Amino Acids on Iron Uptake in Relation to their Effects on Photoperiodic Flowering in Lemna paucicostata 6746

The flowering of Lemna paucicostata 6746 grown on 14-h photoperiodwas enhanced by the addition of high concentrations of ironto the medium, which also increased the endogenous iron concentration.The addition of asparagine, aspartate, glutamate, -alanine,glycine or serine to the medium also increased the endogenousiron level, resulting in the promotion of flowering. In contrast,the addition of cysteine, cystine, glutamine, arginine, threonineor phenylalanine lowered the endogenous iron level, resultingin the inhibition of flowering. Glycine and asparagine added to the medium during an inductive96-h dark period did not promote iron uptake and had no effecton flowering, but when added during the subsequent 120-h lightperiod, they promoted both iron uptake and flowering response.The increase in the endogenous iron level seems to favor floraldevelopment rather than induction of photoperiodic floweringof Lemna paucicostata 6746. (Received September 8, 1986; Accepted March 31, 1987)     

Expression of soybean glycinin subunit precursor cDNAs in Escherichia coli

As the cDNAs encoding A1aB1b and A2B1a subunit precursors of the glycinin A2 subfamily contain a unique NcoI site sequence, (A)CCATGG, occurring at their translation initiation sites, plasmids were constructed to direct the synthesis of those precursor proteins by inserting NcoI/PstI fragments derived from those cDNA clones into the NcoI/PstI-pKK233-2 expression vector in Escherichia coli MV1190, respectively. The resultant plasmids directed the expression of 57-kDa protein components that have molecular masses in agreement with those of the in vitro translation products directed by glycinin A2 subfamily mRNAs, by the addition of isopropyl beta-D-thiogalactoside. These proteins, which comprised as much as 1% of the total bacterial protein, are immunoprecipitable with rabbit antibodies specific for glycinin subunits. This procedure makes glycinin subunits available as a model for studying structure-function relationships in seed proteins using site-directed mutagenesis. This is the first expression of glycinin-like storage protein in E. coli.     

Mitochondrial DNA of the extinct quagga: Relatedness and extent of postmortem change

Sequences are reported for portions of two mitochondrial genes from a domestic horse and a plains zebra and compared to those published for a quagga and a mountain zebra. The extinct quagga and plains zebra sequences are identical at all silent sites, whereas the horse sequence differs from both of them by 11 silent substitutions. Postmortem changes in quagga DNA may account for the two coding substitutions between the quagga and plains zebra sequences. The hypothesis that the closest relative of the quagga is the domestic horse receives no support from these data. From the extent of sequence divergence between horse and zebra mitochondrial DNAs (mtDNAs), as well as from information about the fossil record, we estimate that the mean rate of mtDNA divergence in Equus is similar to that in other mammals, i.e., roughly 2% per million years.     

Distribution and evolution of C4 syndrome inRhynchospora (Rhynchosporeae-Cyperaceae)

In order to elucidate the evolution of C₄ syndrome, the taxonomic relationships, leaf anatomy, and ecological and global distribution of C₃ and C₄ species in the genusRhynchospora were investigated. The anatomical observation for 181 species revealed that 26 C₄ species occurred within theCapitatae group of the subgenusHaplostyleae, a natural group showing highly advanced morphological characteristics, together with several C₃ species. In spite of there being rather few C₄ species, they possessed two kinds of Kranz anatomical structure differing from each other in the location of Kranz cells. Some C₃ species ofCapitatae showed radial arrangement in mesophyll cells surrounding vascular bundles, which is distinguished from typical non-Kranz anatomy. The C₄ species extended their ecological ranges from wet habitats to dry savanna grasslands, while the C₃ species showed the best development in wet habitats. The C₃ species were widespread from tropical to temperate regions with partial range extension into subarctic regions of both hemispheres, showing conspicuously high concentration of species in the New World, but being absent from arid climatic regions. The C₄ species were distributed mostly in tropics and subtropics, showing two separate distributional centers in South and Central America and in Tropical Asia and Australia. The range of C₄ species was nearly completely included in the C₃ range. In conclusion, it seems that inRhynchospora the C₄ syndrome evolved relatively recently, and arose in at least two separate phylogenetic trends in the tropics and the subtropics, more probably in the Neotropics.     

Lattice swelling with the selective digestion of elastic components in single-skinned fibers of frog muscle.

Changes in the 1.0 lattice spacing during trypsin (0.25 micrograms/ml) treatment in mechanically skinned single fibers of frog muscle was examined by an x-ray diffraction method at various sarcomere lengths. The resting tension of a relaxed fiber was decreased by trypsin treatment but the stiffness of a rigor fiber was not, suggesting that elastic components were selectively digested. With progression of the digestion, the lattice spacing increased remarkably at longer sarcomere lengths and finally became independent of the sarcomere length. The increase in the lattice spacing was proportional to the decrease in the resting tension. These results support our previous suggestion (Higuchi, H., and Y. Umazume, 1986, Biophys. J., 50:385-389) that the lattice spacing decreases at long lengths due to compressive force exerted by a lateral elastic component that connects thick filaments to an axial elastic component. Consequently, it is unlikely that the decrease in the lattice spacing is determined by a decrease in the repulsive force between thick and thin filaments with stretching a fiber.