Molecular alteration of a muscarinic acetylcholine receptor system during synaptogenesis

Biochemical properties of the muscarinic acetylcholine receptor system of the avian retina were found to change during the period when synapses form in ovo. Comparison of ligand binding to membranes obtained before and after synaptogenesis showed a significant increase in the affinity, but not proportion, of the high affinity agonist-binding state. There was no change in receptor sensitivity to antagonists during this period. Pirenzepine binding, which can discriminate muscarinic receptor subtypes, showed the presence of a single population of low affinity sites (M2) before and after synaptogenesis. The change in agonist binding was not due to the late development of receptor function; tests for receptor-stimulated phosphatidylinositol turnover and for modulation of agonist binding by guanylylimidodiphosphate showed functional coupling to be present several days prior to the onset of synapse formation. However, detergent-solubilization of membranes eliminated differences in agonist binding between receptors from embryos and hatched chicks, suggesting a developmental change in interactions of the receptor with functionally related membrane components. A possible basis for altered interactions was obtained from isoelectric point data showing that the muscarinic receptor population underwent a transition from a predominantly low pI form (4.25) in 13 day embryos to a predominantly high pI form (4.50) in newly hatched chicks. The possibility that biochemical changes in the muscarinic receptor play a role in differentiation of the system by controlling receptor position on the surface of nerve cells is discussed.     

Hormonal regulation of the alpha-ketoglutarate dehydrogenase complex in the isolated perfused rat liver

The metabolic flux through the alpha-ketoglutarate dehydrogenase reaction in perfused livers was monitored by measuring the rate of 14CO2 production from [1-14C]alpha-ketoglutarate. The rates of 14CO2 production and glucose production from [1-14C]alpha-ketoglutarate were increased with increasing perfusate alpha-ketoglutarate concentrations. Vasopressin, angiotensin II, and the alpha 1-adrenergic agonist phenylephrine stimulated transiently by 2.5-fold the metabolic flux through the alpha-ketoglutarate dehydrogenase reaction in the presence and absence of Ca2+ in the perfusion medium. High concentrations of glucagon (1 x 10(-8) M) and 8-p-chlorophenylthio-cAMP (100 microM) (data not shown) also stimulated transiently the metabolic flux through the alpha-ketoglutarate dehydrogenase reaction. However, lower glucagon concentrations (1 x 10(-9) M) stimulated the rate of 14CO2 production from [1-14C]alpha-ketoglutarate only under conditions optimized to fix the cellular oxidation-reduction state at an intermediate level, when glucagon (1 x 10(-9) M)-mediated elevation of cAMP content was greater than that observed under highly oxidizing and reducing conditions. These data indicate that agonists which increase cytosolic free Ca2+ levels stimulate the metabolic flux through the alpha-ketoglutarate dehydrogenase complex. Furthermore, the data presented here demonstrate for the first time that physiological glucagon concentrations stimulate the metabolic flux through the alpha-ketoglutarate dehydrogenase reaction only under conditions known to be optimal for glucagon-mediated Ca2+ mobilization in the isolated perfused rat liver.     

Regulation of ornithine decarboxylase activity by spermidine and the spermidine analogue N1N8-bis(ethyl)spermidine.

Polyamine biosynthesis in intact cells can be exquisitely controlled with exogenous polyamines through the regulation of rate-limiting biosynthetic enzymes, particularly ornithine decarboxylase (ODC). In an attempt to exploit this phenomenon as an antiproliferative strategy, certain polyamine analogues have been identified [Porter, Cavanaugh, Stolowich, Ganis, Kelly & Bergeron (1985) Cancer Res. 45, 2050-2057] which lower ODC activity in intact cells, have no direct inhibitory effects on ODC, are incapable of substituting for spermidine (SPD) in supporting cell growth, and are growth-inhibitory at micromolar concentrations. In the present study, the most effective of these analogues, N1N8-bis(ethyl)SPD (BES), is compared with SPD in its ability to regulate ODC activity in intact L1210 cells and in the mechanism(s) by which this is accomplished. With respect to time and dose-dependence of ODC suppression, both polyamines closely paralleled one another in their response curves, although BES was slightly less effective than SPD. Conditions of minimal treatment leading to near-maximal ODC suppression (70-80%) were determined and found to be 3 microM for 2 h with either SPD or BES. After such treatment, ODC activity was fully recovered within 2-4 h when cells were re-seeded in drug-free media. By assessing BES or [3H]SPD concentrations in treated and recovered cells, it was possible to deduce that an intracellular accumulation of BES or SPD equivalent to less than 6.5% of the combined cellular polyamine pool was sufficient to invoke ODC regulatory mechanisms. Decreases in ODC activity after BES or SPD treatment were closely paralleled by concomitant decreases in ODC protein. Since cellular ODC mRNA was not similarly decreased by either BES or SPD, it was concluded that translational and/or post-translational mechanisms, such as increased degradation of ODC protein or decreased translation of ODC mRNA, were probably responsible for regulation of enzyme activity. Experimental evidence indicated that neither of these mechanisms seemed to be mediated by cyclic AMP or ODC-antizyme induction. On the basis of the consistent similarities between BES and SPD in all parameters studied, it is concluded that the analogue most probably acts by the same mechanisms as SPD in regulating polyamine biosynthesis.     

Evolution of the immunodominant domain of the circumsporozoite protein gene from Plasmodium vivax. Implications for vaccines

Recent work directed toward the development of a malarial vaccine has focused on the identification and production of the immunodominant repeating peptide of the circumsporozoite protein of the human malaria parasites as an antigen. An important factor which relates to the usefulness of this antigen in a vaccine is the rate at which the molecule changes in sequence. We have determined the sequence and arrangement of the repeating epitope of the circumsporozoite protein gene from a Plasmodium vivax isolate from La Paz, El Salvador (Sal-I). This is compared with a portion of the previously published sequence of the circumsporozoite protein gene from a P. vivax isolate from Belém, Brazil. The genes appear to be very similar in the repeat region. There are 20 similar repeating units in the El Salvador strain and only 19 units are conserved in the Brazilian strain. Following this there are degenerate repeats in both strains. Even the pattern of silent mutations in the repeat area are similar; however, they are not necessarily in the identical location and appear to have shifted. The data suggest that the repeat region of these genes may be evolving by an accelerated mechanism(s). Such a phenomenon could severely decrease the long-term efficacy of a repeat-based anti-sporozoite vaccine.     

Frequency of Escherichia coli O157:H7 isolation from stool specimens

During a 6-month period, 7252 faeces specimens were examined for Escherichia coli serotype O157:H7. Forty-nine specimens (0.7%) from 19 patients yielded this organism. Escherichia coli O157:H7 was the third most frequently isolated bacterial pathogen, following Campylobacter jejuni and (or) Salmonella sp. Although regional variation between laboratories determined whether Campylobacter jejuni or Salmonella was the primary bacterial pathogen isolated, E. coli O157:H7 was consistently isolated more frequently than either Shigella or Yersinia enterocolitica.     

Effect of butaclamol enantiomers on hypothalamic tyrosine hydroxylase in the rat brain

The authors demonstrate stereospecificity of the action of butaclamol enantiomers on substrate inhibition of hypothalamic tyrosine hydroxylase (TH) and regulation of the tyrosine hydroxylase response by the presynaptic membrane (presynaptic receptors) of rat hypothalamus synaptosomes under membrane activation with dopamine. The effect of (+)-butaclamol on the substrate inhibition of TH was noticeable at a concentration of 10(-8)M, reaching a maximum at 10(-5)M. (-)-Butaclamol administered at the same concentrations did not influence the substrate inhibition of the enzyme. (+)-Butaclamol added to the incubation medium containing hypothalamic synaptosomes concurrently with dopamine (10(-5)M) completely blocked the regulatory action of the latter on TH, with this action mediated via presynaptic receptors. (-)-Butaclamol (10(-5)M) antagonized the action of dopamine under the same conditions. The data obtained indicate high stereo-specificity of butaclamol enantiomers as regards their effect on presynaptic regulation of TH, suggesting that elimination of the substrate inhibition of hypothalamic TH is a stereoselective effect of neuroleptics and can be a prognostically important criterion in the appraisal of compounds with potential neuroleptic activity.     

Isolation of microsatellite loci in the Capricorn silvereye,Zosterops lateralis chlorocephalus (Aves: Zosteropidae)

The Capricorn silvereye (Zosterops lateralis chlorocephalus) is ideally suited to investigating the genetic basis of body size evolution. We have isolated and characterized a set of microsatellite markers for this species. Seven out of 11 loci were polymorphic. The number of alleles detected ranged from two to five and observed heterozygosities between 0.12 and 0.67. One locus, ZL49, was found to be sex‐linked. This moderate level of diversity is consistent with that expected in an isolated, island population.     

Identification of N5-methyl-N5-formyl-2,5,6-triamino-4-hydroxypyrimidine as a major adduct in rat liver DNA after treatment with the carcinogens, N,N-dimethylnitrosamine or 1,2-dimethylhydrazine

Human Tamm-Horsfall urinary glycoprotein from an individual of the blood group Sd(a+) phenotype was tritium-labelled by treatment with galactose oxidase and sodium boro[3H]hydride and was then digested with endo-beta-galactosidase. A series of dialysable, labelled fragments was released from which a pentasaccharide was isolated that strongly inhibited the agglutination of Sd(a+) red cells by human anti-Sda serum and hence contained the Sda determinant structure. Reduction, methylation analysis and sequential exo-glycosidase digestion established the structure of the pentasaccharide as: GalNAc beta(1 leads to 4)[NeuAc(2 leads to 3)]Gal beta(1 leads to 4)GlcNAc beta(1 leads to 3)Gal     

Restriction fragment length polymorphisms of horse class II MHC genes observed using various human alpha-and beta-chain cDNA probes

Genomic DNA isolated from 20 horses was digested with up to six restriction endonucleases and subjected to southern blot hybridization analysis using various human class II alpha- and beta-chain cDNA probes. A high degree of restriction fragment length polymorphism (RFLP) was found for the DQ alpha, DP beta, DQ beta and DR beta probes, about 20 polymorphic bands being detected for each. DR alpha showed 2-4 polymorphic bands, whereas no evidence for DP alpha-like genes was found. A number of correlations of RFLPs with individual alloantisera were apparent.     

Surface Plasmodium sugar-binding components evidenced by fluorescent neoglycoproteins

A sugar-binding component was shown to be present at the surface of endoerythrocytic Plasmodium berghei and P. chabaudi stages and merozoites by means of a panel of neoglycoproteins using fluorescence microscopy and flow cytofluorometry. The protein nature of this material was ascertained by the loss of sugar-binding capacity upon trypsin treatment. This lectin-like protein primarily bound neoglycoprotein-borne N-acetylglucosamine and secondarily bound neoglycoprotein-borne alpha-D-glucose, beta-D-galactose and alpha-L-fucose. These results suggest the presence of at least one type of lectin-like protein with an extended binding site accomodating several sugar units, and define its localization on the parasite surface.