Co-distribution of annexin VI and actin in secretory ameloblasts and odontoblasts of rat incisor

Summary Annexin VI and actin were detected by immunoblot analysis in the enamel- and dentin-related portions of dental tissues. Annexin VI was found mainly in the particulate fraction whereas actin was detected in both the soluble and particulate fractions. By immunoelectron microscopy, annexin VI antibodies conjugated with colloidal gold were seen to label the mitochondria, the cytosol and the nucleus of secretory ameloblasts and odontoblasts of rat incisor. In the processes of these cell, the plasmalemmal undercoat was labeled. Antiactin antibodies labeled the desmosome-like junctions, the cytosol, and the mitochondria of the cell bodies. Extensive labeling was seen at the periphery of the Tomes' processes and odontoblast processes. These results suggest that annexin VI may play a role in Ca²⁺-regulation in the cell bodies, especially as a calcium receptor protein in the mitochondria. Moreover, annexin VI and actin seem to be co-distributed in secretory processes. Thus, these proteins might be both involved in exocytotic and endocytotic events.     

Structure and expression of the Chlorobium vibrioforme hemA gene

The green sulfur bacterium, Chlorobium vibrioforme, synthesizes the tetrapyrrole precursor, -aminolevulinic acid (ALA), from glutamate via the RNA-dependent five-carbon pathway. A 1.9-kb clone of genomic DNA from C. vibrioforme that is capable of transforming a glutamyl-tRNA reductase-deficient, ALA-dependent, hemA mutant of Escherichia coli to prototrophy was sequenced. The transforming C. vibrioforme DNA has significant sequence similarity to the E. coli, Salmonella typhimurium, and Bacillus subtilis hemA genes and contains a 1245 base open reading frame that encodes a 415 amino acid polypeptide with a calculated molecular weight of 46174. This polypeptide has over 28% amino acid identity with the polypeptides deduced from the nucleic acid sequences of the E. coli, S. typhimurium, and B. subtilis hemA genes. No sequence similarity was detected, at either the nucleic acid or the peptide level, with the Rhodobacter capsulatus or Bradyrhizobium japonicum hemA genes, which encode ALA synthase, or with the S. typhimurium hemL gene, which encodes glutamate-1-semialdehyde aminotransferase. These results establish that hemA encodes glutamyl-tRNA reductase in species that use the five-carbon ALA biosynthetic pathway. A second region of the cloned DNA, located downstream from the hemA gene, has significant sequence similarity to the E. coli and B. subtilis hemC genes. This region contains a potential open reading frame that encodes a polypeptide that has high sequence identity to the deduced E. coli and B. subtilis HemC peptides. hemC encodes the tetrapyrrole biosynthetic enzyme, porphobilinogen deaminase, in these species. Preliminary evidence was obtained for the existence of a 3.0-kb polycistronic meassge that includes the hemA sequence, in exponentially growing C. vibrioforme cells. Results of condon usage analysis for the C. vibrioforme hemA gene indicate that green sulfur bacteria are more closely related to purple nonsulfur bacteria than to enteric bacteria. Sequences corresponding to a polyadenylation signal and a poly(A) attachment site were found immediately downstream from the 3 end of the hemA open reading frame.     

Margaret Mead and Samoa: Coming of Age in Fact and Fiction

Derek Freeman's 1983 critique of Margaret Mead's Coming of Age in Samoa has prompted one of the most heated debates in recent anthropological memory. Yet even Mead's defenders have generally accepted the view that she saw Samoa as a romantic paradise. Here I argue that a careful reading of Coming of Age shows quite a different picture. In my reanalysis, Mead's work emerges as complex and somewhat enigmatic, with facile conclusions standing in contrast to much rich and sensitive ethnography. My goal in this article is to highlight what Mead actually said, pointing up the notable discrepancy between the popular perception and her actual account.     

Bovine serum brevin. Purification by hydrophobic chromatography and properties

Brevin, an actin-severing protein present in serum from numerous mammals, has been purified to homogeneity from bovine serum, using hydrophobic chromatography as the last purification step. The physicochemical parameters of brevin have been established and some of them studied in the absence and presence of Ca2+. Brevin exhibits an apparent Stokes radius, Rs, of 3.4 nm, an intrinsic sedimentation coefficient S degrees 20, W, of 4.8 S and 4.4 S in the absence and presence of Ca2+ respectively, indicative of calcium-induced conformational change. The native molecular mass of brevin was found to be 68 kDa and the hydrodynamic data suggest that the protein is an asymmetric molecule. Sedimentation equilibrium studies demonstrated that Ca2+ affects the shape (asymmetry) of brevin without altering its molecular mass. Limited tryptic and chymotryptic digestion of brevin distinguishes the Ca2+-induced conformation from the EGTA one. No change in the electrophoretic migration of brevin was seen upon Ca2+ addition. Several isoforms were detected by two-dimensional gel electrophoresis. Brevin increases the rate of nucleation of actin but decreases the rate of elongation of the filaments and the steady-state viscosity of F-actin in substoichiometric amounts, as measured by viscometric assays under high shear conditions. Electron microscopic examination documents these effects. Brevin produces shorter actin filaments and binds to the 'barbed' end of filaments to which monomers add preferentially during elongation, as demonstrated by indirect immunogold staining of antibodies against brevin. Filament elongation occurs only at the slowly growing end. An enzyme-linked immunosorbent assay was developed and used to detect and quantify brevin and related proteins in extracts of different bovine cells and tissues. Liver and smooth muscles were found to contain the highest amounts of the severing protein.     

Application of Response Surface Methodology to Evaluation of Bioconversion Experimental Conditions

Using Candida tenuis, a yeast isolated from the digestive tube of the larva of Phoracantha semipunctata (Cerambycidae, Coleoptera), we were able to demonstrate the bioconversion of citronellal to citronellol. Response surface methodology was used to achieve the optimization of the experimental conditions for that bioconversion process. To study the proposed second-order polynomial model, we used a central composite experimental design with multiple linear regression to estimate the model coefficients of the five selected factors believed to influence the bioconversion process. Only four were demonstrated to be predominant: the incubation pH, temperature, time, and the amount of substrate. The best reduction yields (close to 90%) were obtained with alkaline pH conditions (pH 7.5), a low temperature (25°C), a small amount of substrate (15 μl), and short incubation time (16 h). This methodology was very efficient: only 36 experiments were necessary to assess these conditions, and model adequacy was very satisfactory as the coefficient of determination was 0.9411.     

The comparative effects of vitamin deficiency on development and on adult fecundity of Tribolium castaneum

When larvae of Tribolium castaneum were reared on diets deficient in thiamine, pyridoxine or riboflavin mortality was high and the rate of development was slow. The few surviving larvae did attain the same final stage as larvae developing on an all-vitamin control. On diets deficient in nicotinic acid, calcium pantothenate or choline chloride all aspects of development were impaired and no pupation occurred. The negative effects of folic acid deficiency were more pronounced in the pupal stage than in the larval instars. The dietary deficiency of folic acid, choline chloride or thiamine, had no apparent effect on adult fecundity, and a dietary deficiency of any one of the seven vitamins assayed did not adversely affect egg fertility.

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Résumé Une mortalité importante a été constatée chez des larves de Tribolium castaneum élevées sur des régimes déficitaires en thiamine, pyridoxine et riboflavine. Le développement a été ralenti d'une façon considérable, mais les larves qui ont survécu sont arrivées au même stade final que les larves témoins nourries avec toutes les vitamines. Tous les autres régimes alimentaires ont été moins adéquates que celui contenant un supplément de levure. L'effet de l'absence de l'acide nicotinique, du pantothenate de calcium ou bien du chlorure de choline a été encore plus net, car les larves ne se sont pas nymphosées. Cet effet prononcé de l'insuffisance du chlorure de choline contraste avec la réaction de Tribolium confusum à l'absence de chlorure de choline dans le régime alimentaire.Le développement larvaire a été peu affecté par l'absence de l'acide folique. Mais, durant la nymphose, les effets négatifs se manifestent davantage encore. L'absence de pyridoxine, riboflavine, acide nicotinique ou pantothenate du calcium a réduit d'une façon importante le taux initial de la fécondité des adultes de T. castaneum. L'absence de l'acide folique, chlorure de choline ou thiamine n'a pas été marquée par un effet semblable. La fertilité des ufs n'a pas été affectée par le manque d'une vitamine quelconque.Ces résultats indiquent que le chlorure de choline et la thiamine sont nécessaires pour le développement larvaire, mais qu'elles sont peu importantes pour la vitalité des adultes. Les réserves en certaines vitamines essentielles chez les nymphes suffisent donc aux exigences des adultes, au moins pendant quelques mois après leur éclosion.

     

Purification and properties of a low-redox-potential tetraheme cytochrome c3 from Shewanella putrefaciens.

Shewanella putrefaciens is a facultatively anaerobic bacterium in the gamma group of the proteobacteria, capable of utilizing a wide variety of anaerobic electron acceptors. An examination of its cytochrome content revealed the presence of a tetraheme, low-redox-potential (E'o = -233 mV), cytochrome c-type cytochrome with a molecular mass of 12,120 Da and a pI of 5.8. The electron spin resonance data indicate a bis-histidine coordination of heme groups. Reduction of ferric citrate was accompanied by oxidation of the cytochrome. The biochemical properties suggested that this protein was in the cytochrome c3 group, which is supported by N-terminal sequence data up to the first heme binding site.     

The common origins of the pigments of life—early steps of chlorophyll biosynthesis

The complex pathway of tetrapyrrole biosynthesis can be dissected into five sections: the pathways that produce 5-aminolevulinate (the C-4 and the C-5 pathways), the steps that transform ALA to uroporphyrinogen III, which are ubiquitous in the biosynthesis of all tetrapyrroles, and the three branches producing specialized end products. These end products include corrins and siroheme, chlorophylls and hemes and linear tetrapyrroles. These branches have been subjects of recent reviews. This review concentrates on the early steps leading up to uroporphyrinogen III formation which have been investigated intensively in recent years in animals, in plants, and in a wide range of bacteria.Abbreviations ALA 5-aminolevulinic acid - ALAS 5-aminolevulinic acid synthase - GR glutamyl-tRNA reductase - GSA glutamate-1-semialdehyde - GSAT glutamate-1-semialdehyde aminotransferase - HMB hydroxymethylbilane - PBG porphobilinogen - PBGD porphobilinogen deaminase - PBGS porphobilinogen synthase - URO uroporphyrin - URO'gen uroporphyrinogen - US uroporphyrinogen III synthase