Control of sugar transport in human fibroblasts independent of glucose metabolism or carrier-substrate interaction

Transport regulation by different metabolizable and nonmetabolizable sugars was studied in human fibroblasts. Sugars were classed as glucose-like (D-mannose, 3-0-methyl-D-glucose, thio-D-glucose, and D-allose) and starvation-like (D-galactose, D-fructose, L-glucose, D-xylose, 6-deoxy-D-glucose and 2-deoxy-D-glucose) based on their competence in curbing glucose starvation enhanced transport. No significant correlation existed between the ability of a sugar to curb hexose transport and the KI of that sugar in inhibiting hexose transport. Independence of the transport curb from glucose metabolism was observed since nonmetabolizable analogs of D-glucose when substituted for D-glucose in the culture medium effected glucose [i.e. 3-0-methyl-D-glucose (3-OMG)] and starvation-like (i.e. 6- and 2-deoxy-D-glucose) effects. The KI of inhibition pf 2-deoxy-D-glucose transport for 3-OMG was 8.5 mM, similar to those obtained for 6-deoxyglucose and 2-deoxyglucose on 2-deoxyglycose transport (7.5 and 3.5 mM, respectively) and on 3-0-methylglucose transport (3.5 and 2.5 mM, respectively). An equimolar mixture of D-glucose and 3-OMG (5.55 mM each) was more effective than 11.1 mM D-glucose or 3-OMG alone in curbing hexose transport or reversing hexose starvation induced increases in transport. The effect of 3-OMG may be independent of glucose metabolism but it is possible that 3-OMG structurally mimics a metabolite of glucose that may interact with intracellular regulators of carrier degradation and or expression.     

Blockade of a motor response by cholinergic stimulation of the toad midbrain tegmentum

Application of an acid solution to the dorsal skin of conscious toads having intact nervous system induces a scratching reflex and escape movements, as well as autonomic alterations (hypertension and tachycardia) that are part of the defense response. The motor components of this response are abolished or reduced by microinjection of 60, 30, 15 or 7.5 ng carbachol into the midbrain tegmentum. The cardiovascular components, however, continue to be present, although their amplitude is reduced. The depression of the motor response is statistically significant up to 15 minutes for the 60 ng dose, up to 10 minutes for the 15 and 30 ng doses, and only up to 5 minutes for the 7.5 ng dose. The data suggest that the midbrain tegmentum may modulate the reflex motor response triggered by a noxious stimulus and also participate in the organization of the escape movements. The importance of cholinergic agents in this modulation is discussed. The persistence of the cardiovascular component of the response shows the importance of this parameter as an indicator of alert situations.     

Sustained sensitivity modifications induced by brief length perturbations in the crayfish slowly adapting stretch receptor

These experiments in the slowly adapting stretch receptor of crayfish test the effects of brief length perturbations (i.e., pulses) when presented in isolation at different constant elongations or superimposed on trapezoidal stretches of different amplitudes. Within "in vivo" lengths, during static responses, perturbations reduced firing rates to below control values and, in extreme cases, could silence the receptor. This effect, or "down-step," was sustained, occurred above a threshold pulse amplitude and background stretch, and increased with both stimulus characteristics, but was not present during dynamic responses. Beyond "in vivo" lengths, and in a few cases within those limits but close to the extremes, the receptor was silent but perturbations could restore activity. Lengthening pulses were more effective than shortening ones in generating after-effects. Perturbations change, during indefinitively long periods, the receptor's length or static sensitivity acting as a negative feedback which tends to maintain the discharge rate within fixed values. Perturbations disclose marked nonlinearities, which suggest that the classical view of a proportional control in the reflex loop in which the receptor participates may not operate in natural conditions.     

Meiotic behaviour of Un,D and R genomes in the amphiploid Aegilops ventricosa -Secale cereale and the parental species

Summary Meiotic pairing frequencies of the Un and D genomes of Ae. ventricosa and the R of S. cereale could be easily established at metaphase I in Aegilops ventricosa — Secale cereale amphiploid plants as well as in its parental species by using the C-banding technique procedure. The results show a high diminution of chromosome pairing for all genomes in the amphiploid with respect to its parental species probably due to C-heterochromatin content and/or genotypic or cryptic interactions between the three genomes.     

In vitro synthesis of full-length influenza virus complementary RNA.

Influenza virus-specific RNA has been synthesized in vitro, using cytoplasmic or microsomal fractions of influenza virus-infected MDCK cells. The RNA polymerase activity was stimulated 5-30 times by priming with ApG. About 20-30% of the product was polyadenylated. Most of the in vitro product was of positive polarity, as shown by hybridization to strand specific probes and by T1 fingerprinting of the poly(A)+ and poly(A)- RNA segments encoding haemagglutinin and nucleoprotein. The size of poly(A)- RNA segments, determined on sequencing gels, was indistinguishable from that of virion RNA, whereas poly(A)+ RNA segments contain poly(A) tails approximately 50 nucleotides long. The size of in vitro synthesized RNA segments was also determined by gel electrophoresis of S1-treated double-stranded RNAs, obtained by hybridization of poly(A)+ or poly(A)- RNA fractions with excess of unlabelled virion RNA. The results of these experiments indicate that poly(A)- RNA contains full-length complementary RNA. This conclusion is further substantiated by the presence of additional oligonucleotides in the T1 fingerprints of in vitro synthesized poly(A)- haemagglutinin or nucleoprotein RNA, selected by hybridization to cloned DNA probes corresponding to the 3' termini of the genes.     

Division of temperature-sensitive Streptococcus faecium mutants after return to the permissive temperature

The regrowth of 27 temperature-sensitive division mutants of Streptococcus faecium ATCC 9790 was examined after various periods of incubation at the nonpermissive temperature. Several of the mutants blocked at various stages of septum formation or of daughter-cell separation divided in a partially or completely synchronous way after a short incubation at the nonpermissive temperature. All four lytic mutants blocked early in the cell division cycle divided at a normal rate after a brief lag.     

Location of O-acetyl groups in the acidic d-xylan of mimosa scabrella (bracatinga). A study of O-acetyl group migration

Extraction with dimethyl sulfoxide of wood-meal of the stem of bracatinga (Mimosa scabrella), a south Brazilian hardwood, that was defatted and delignified by treatment with aqueous chlorine at 0–5° followed by extraction with cold ethanol, gave a soluble O-acetylated 4-O-methyl-d-glucurono-d-xylan having (1→4)-linked β-d-xylopyranosyl residues that were unsubstituted (65%) and 2-O-(14%), 3-O- (16%), and 2,3-di-O-acetylated (5%), as determined by methylation analysis. Another preparation obtained by use of refluxing ethanol in the delignification process showed neither removal nor migration of acetyl groups. By comparison with synthetic, partly O-acetylated d-xylans of known composition, ¹³C-n.m.r. spectroscopy indicated that O-acetyl group migration does not occur during treatment with cold aqueous chlorine, refluxing ethanol, or water at 70°. Methyl 2-O-acetyl-4-O-methyl-β-d-xylopyranoside (6) was also unaffected by aqueous chlorine. O-Acetyl group migration took place more readily in aqueous and dimethyl sulfoxide solutions of 6 than of O-acetyl-d-xylans. The lowest temperatures at which migration was observed in monosaccharides was at 50 and 70° for solutions in D₂O and (CD₃)₂SO, respectively.     

Antagonism of diazepam-induced feeding in rats by antisera to opioid peptides

Diazepam-induced feeding in rats is antagonized not only by the opiate antagonist naloxone but also intraventricular administration of specific antisera to the endogenous opioid peptides met-enkephalin or beta-endorphin. Pituitary beta-endorphin is probably not implicated in the diazepam effect since blockade with the glucocorticoid dexamethasone of the release of beta-endorphin from the anterior pituitary does not modify the diazepam-induced feeding, which is however prevented by TRH, a suggested physiological antagonist of some of the effects of opioid peptides. The possible central participation of both beta-endorphin and met-enkephalin in the ingestive behavior induced by diazepam gives further support to the postulated physiological role of endogenous opioids in appetite regulation.     

Effect of Phospholipase Digestion and Lysophosphatidylcholine on Dopamine Receptor Binding

[3H]Spiperone specific binding by microsomal membranes isolated from sheep caudate nucleus is decreased by trypsin and phospholipase A2 (Vipera russeli), but is insensitive to neuraminidase. The inhibitory effect of phospholipase A2 is correlated with phospholipid hydrolysis. After 15 min of phospholipase (5 micrograms/mg protein) treatment, a maximal effect is observed; the maximal lipid hydrolysis is about 56% and produces 82% reduction in [3H]spiperone binding. Equilibrium binding studies in nontreated and treated membranes showed a reduction in Bmax from a value of 388 +/- 9.2 fmol/mg protein before phospholipase treatment to a value of 52 +/- 7.8 fmol/mg protein after treatment, but no change in affinity (KD = 0.24 +/- 0.042 nM) was observed. Albumin washing of treated membranes removes 47% of lysophosphatidylcholine produced by phospholipid hydrolysis without recovering [3H]spiperone binding activity. However, the presence of 2.5% albumin during phospholipase A2 action (1.5 micrograms/mg protein) prevents the inhibitory effect of phospholipase on [3H]spiperone binding to the membranes, although 28% of the total membrane phospholipid is hydrolysed. Lysophosphatidylcholine, a product of phospholipid hydrolysis, mimics the phospholipase A2 effect on receptor activity, but the [3H]spiperone binding inhibition can be reversed by washing with 2.5% defatted serum albumin. Addition of microsomal lipids to microsomal membranes pretreated with phospholipase does not restore [3H]spiperone stereospecific binding. It is concluded that the phospholipase-mediated inhibition of [3H]spiperone binding activity results not only from hydrolysis of membrane phospholipids, but also from an alteration of the lipid environment by the end products of phospholipid hydrolysis.     

Some observations on the urea-degrading enzyme of the diatom Cyclotella cryptica and the role of nickel in its production

The urea-degrading enzyme of Cyclotella cryptica was testedin crude cell-free extracts for effects from chemical reagentsknown to distinguish between urease and ATP:urea amidolyase.Inhibition of the enzyme by hydroxyurea and its indifferenceto added ATP, Mg²⁺ or K⁺ avidin or biotin clearly characterizedthe enzyme as urease (EC 3.5.1.5 [EC] ). The Cyclotella urease wasunaffected by thiourea addition, as was also the growth of thediatom in the presence of this substrate analogue. Indirectevidence was obtained from growth studies of the diatom andcorresponding urease production showing that the enzyme: (i)contains Ni²⁺ tightly bound to an apoprotein; (ii) is producedconstitutively even from growth on nitrate and does not requireextracellular urea for its synthesis, although quantitativelythe activity is greatest from growth on urea. It is concludedthat Cyclotella urease is a Ni²⁺ constitutive enzyme similarin many respects to those previously reported from Phaeodactylumtricornutwn and Tetraselmis maculata.