STRUCTURAL ALTERATIONS OF AMINO ACIDS AT THE LEVEL OF AMINOACYL-tRNAS: IDENTIFICATION OF THE TRANSFORMATION PRODUCTS OF DICARBOXYLIC AMINO ACIDS

Abstract— Glutamyl-, glutaminyl-, aspartyl- and asparaginyl-tRNAs were separated into different isoacceptor species by reverse phase column chromatography. RNase hydrolysates of any of the isoacceptor [¹⁴C]aminoacyl-tRNAs for a given amino acid gave radioactivity profiles, on paper electrophoresis, very similar to unfractionated tRNA. This suggested a lack of tRNA specificity for the transformation reaction involving the aminoacyl moieties of asparaginyl and glutaminyl-tRNAs. GnP₂ and AnP₂ detected in the products of deaminoacylation of glutaminyl and asparaginyl-tRNA showed a number of properties in common with GnE₃ and AnE₃ present in the RNase hydrolysates of the same tRNAs. Thus, GnP₂ and GnE₃ chromatographed in the same position in the phenol: water solvent and both yielded glutamate on acid hydrolysis and a mixture of glutamine and isoglutamine on alkaline hydrolysis. Similarly, AnP₂ and AnE₃ had the same R_F value in phenol :water chromatography and gave aspartate or a mixture of asparagine and isoasparagine when hydrolyzed with acid or alkali. On the basis of these results and other evidence, GnP₂ and GnE₃ were assigned the structure, α-aminoglutarimide; AnP₂ and AnE₃ were identified as α-aminosuccinimide. These cyclic compounds are presumed to be formed by nucleophilic attack of the amide nitrogen of asparagine or glutamine on the carbon of the aminoacyl ester carbonyl group. The cyclization-deesterification appeared to be facilitated by RNase hydrolysis of aminoacyl-tRNA indicating that the aminoacyl-tRNA is probably more resistant to this reaction than aminoacyladenosine. Neither the imides nor the amino acid isoamides were detected in the reaction mixture in which aminoacylation of tRNA was performed, suggesting that a mechanism may exist for inhibition of the cyclization reaction under conditions of active aminoacylation.     

Histopathologie de l'action de la δ-endotoxine deBacillus thuringiensis var.Israelensis sur les larves d'Aedes aegypti (Dip.:Culicidae)

Résumé L'ingestion de la δ-endotoxine deBacillus thuringiensis Berliner sérotype H 14 par les larves d'Aedes aegypti L. est suivie par l'apparition d'importantes lésions au niveau de l'intestin moyen. Les dégats ont une amplitude et une vitesse plus ou moins grandes suivant les types cellulaires du mesenteron, mais se traduisent toujours par une hypertrophie cellulaire suivie d'une lyse de l'épithélium.

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Summary Ingestion of theBacillus thuringiensis Berliner sérotype H-14 δ-endotoxin byAedes aegypti L. larvae is followed by important lesions at the midgut level. The severity and speed of injury are dependent upon the cellular types of the mesenteron, but are always expressed by a cellular hypertrophy followed by an epithelial lysis.

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Cette étude a bénéficié d'une aide financière du Programme Spécial PNUD — Banque Mondiale —OMS de Recherche et de Formation concernant les maladies tropicales.     

The rapid effects of 1,25-dihydroxyvitamin D3 require the vitamin D receptor and influence 24-hydroxylase activity: studies in human skin fibroblasts bearing vitamin D receptor mutations

If both rapid and genomic pathways may co-exist in the same cell, the involvement of the nuclear vitamin D receptor (VDR) in the rapid effects of 1,25-dihydroxyvitamin D(3) (1,25-(OH)(2)D(3)) remains unclear. We therefore studied rapid and long term effects of 1,25-(OH)(2)D(3) in cultured skin fibroblasts from three patients with severe vitamin D-resistant rickets and one age-matched control. Patients bear homozygous missense VDR mutations that abolished either VDR binding to DNA (patient 1, mutation K45E) or its stable ligand binding (patients 2 and 3, mutation W286R). In patient 1 cells, 1,25-(OH)(2)D(3) (1 pm-10 nm) had no effect on either intracellular calcium or 24-hydroxylase (enzyme activity and mRNA expression). In contrast, cells bearing the W286R mutation had calcium responses to 1,25-(OH)(2)D(3) (profile and magnitude) and 24-hydroxylase responses to low (1 pm-100 pm) 1,25-(OH)(2)D(3) concentrations (activity, CYP24, and ferredoxin mRNAs) similar to those of controls. The blocker of Ca(2+) channels, verapamil, impeded both rapid (calcium) and long term (24-hydroxylase activity, CYP24, and ferredoxin mRNAs) responses in patient and control fibroblasts. The MEK 1/2 kinase inhibitor PD98059 also blocked the CYP24 mRNA response. Taken together, these results suggest that 1,25-(OH)(2)D(3) rapid effects require the presence of VDR and control, in part, the first step of 1,25-(OH)(2)D(3) catabolism via increased mRNA expression of the CYP24 and ferredoxin genes in the 24-hydroxylase complex.     

Voluntary running exercise prevents β-cell failure in susceptible islets of the Zucker diabetic fatty rat

Physical activity improves glycemic control in type 2 diabetes (T2D), but its contribution to preserving β-cell function is uncertain. We evaluated the role of physical activity on β-cell secretory function and glycerolipid/fatty acid (GL/FA) cycling in male Zucker diabetic fatty (ZDF) rats. Six-week-old ZDF rats engaged in voluntary running for 6 wk (ZDF-A). Inactive Zucker lean and ZDF (ZDF-I) rats served as controls. ZDF-I rats displayed progressive hyperglycemia with β-cell failure evidenced by falling insulinemia and reduced insulin secretion to oral glucose. Isolated ZDF-I rat islets showed reduced glucose-stimulated insulin secretion expressed per islet and per islet protein. They were also characterized by loss of the glucose regulation of fatty acid oxidation and GL/FA cycling, reduced mRNA expression of key β-cell genes, and severe reduction of insulin stores. Physical activity prevented diabetes in ZDF rats through sustaining β-cell compensation to insulin resistance shown in vivo and in vitro. Surprisingly, ZDF-A islets had persistent defects in fatty acid oxidation, GL/FA cycling, and β-cell gene expression. ZDF-A islets, however, had preserved islet insulin mRNA and insulin stores compared with ZDF-I rats. Physical activity did not prevent hyperphagia, dyslipidemia, or obesity in ZDF rats. In conclusion, islets of ZDF rats have a susceptibility to failure that is possibly due to altered β-cell fatty acid metabolism. Depletion of pancreatic islet insulin stores is a major contributor to islet failure in this T2D model, preventable by physical activity.     

Physiological responses to heat strain: A study on personal monitoring for young workers

Heart rate, increased body-core temperature and sweating are the physiological responses to heat stress and they are collectively known as physiological strain. Our goal was to study levels of physiological strain in young farm workers aged 15–21 y. We also verified that heart rate is the response that exceeds threshold limits earliest as seen in previous studies. Personal monitoring for heat-strain measures directly physiological strain as it occurs and gives further information about each worker's state. When estimating levels of physiological strain, certain limits concerning heart rate were adjusted considering the young ages of the workers studied.     

Taxonomic distribution of isoenzymes of dehydroquinate hydrolyase in the angiosperms

The distribution of a dehydroquinate hydrolase (E.C. 4.2.1.10) isoenzyme activated by shikimic acid was studied in angiosperms through a simple diagnos     

Malate Uptake into Isolated Vacuoles from Catharanthus roseus Cells: Role of the Membrane Potential

The mechanisms involved in the transport of malate into isolated vacuoles of Catharanthus roseus (L.) cells were investigated with special reference to the effects of induced changes in membrane potential and surface charges of the tonoplast. For this purpose, thiocyanate (SCN^?), a highly permeant anion often used as a membrane potential probe, was extensively exploited. In the absence of Mg-ATP, the low accumulation ratio of ¹⁴C SCN^? could be related to the presence of negative charges at the outer surface of the tonoplast exerting a screening effect on the displacement of lipophilic anionic species. Nevertheless, malate was taken up continuously by vacuoles supporting the concept of a transport component which facilitates its transfer through the tonoplast. From experiments showing the pH dependence of malata uptake, it is suggested that the protonated form of the transporter is implicated in this process. Moreover, when the vacuoles are energized by Mg-ATP, the study of the equilibrium distribution of ¹⁴C SCN^? indicated an inside positive membrane potential difference. Advantage was taken of these results to modulate the membrane potential with high levels of thiocyanate. The data obtained demonstrate that malate uptake results from electrophoretic movement in response to the positive potential difference.