Effects of Thyroxine on Methionine Adenosyltransferase Activity in Rat Cerebral Cortex and Cerebellum During Postnatal Development

Abstract: Methionine adenosyltransferase (MAT) activity was evaluated in cerebral cortex and cerebellum in controls and in rats treated with thyroxine. In controls the enzyme showed a different pattern in cerebral cortex and cerebellum during neonatal and late suckling periods. Hyperthyroid rats showed a significant increase of the enzyme in cerebral cortex only at the 2nd day of the neonatal period; in cerebellum the developmental pattern of MAT in neonatal period was anticipated temporally by 2–4 days. During the late suckling period thyroxine treatment produced in cerebellum a significant decrease in MAT activity at the 15th day after birth. From these data, we propose that hyperthyroidism may cause precocious induction of MAT both in cerebral cortex and in cerebellum and that the increased availability of S -adenosyll-methionine during the neonatal period could be related to its utilization also in polyamine biosynthesis.     

Peptaibol antibiotics: Conformational preferences of synthetic emerimicin fragments

The ir absorption and CD conformational analyses of solutions of the protected 2–9 fragment of the peptaibol antibiotics emerimicins III and IV \documentclass{article}\pagestyle{empty}\begin{document}$ \rlap{--} (Aib_3 \rlap{--} )L - Val - Gly - L - Leu\rlap{--} (Aib_2 \rlap{--} ) $\end{document} and related short sequences are consistent with the presence of a right-handed α-helix for the octapeptide, while the tri-, tetra-, and pentapeptides adopt a 3₁₀-helix, either right- or left-handed, depending on the amino acid sequences. The structural preferences of solid-state \documentclass{article}\pagestyle{empty}\begin{document}$ Z\rlap{--} (Aib_3 \rlap{--} )L - Val - OMe $\end{document} and \documentclass{article}\pagestyle{empty}\begin{document}$ Z\rlap{--} (Aib_3 \rlap{--} )L - Val - Gly - OMe $\end{document} have been determined by x-ray diffraction. In accord with the solution data, incipient 3₁₀-helices, formed by two and three β-turns, have been found for the tetra- and pentapeptides, respectively. The tetrapeptide helix has the left-handed screw sense, while that of the pentapetide is right-handed, thus confirming the conclusions of the CD analysis of the solution.     

Preferred conformations of peptides containing α,α-disubstituted α-amino acids

The conformational preferences of linear peptides containing α,α-disubstituted α-amino acids, derived from the crystal structures of 28 compounds, are reviewed. In particular, the sensitivity of peptide conformation to the geometry of these unusual amino acids is underlined. We also consider possible future directions of research, which, we hope, will result in a complete understanding of the structures adopted by peptaibol antibiotics.     

Effect of Fish Oil and Coconut Oil on Antioxidant Defence System and Lipid Peroxidation in Rat Liver

Diets high in fish oil containing polyunsaturated fatty acids of the n-3 family. have been suggested to decrease the risk of cardiovascular disease. However these lipids are highly susceptible to oxidative deterioration. In order to investigate the influence of n-3 fatty acids on oxidative status, the effect of feeding rats with fish oil or cocunut oil diets was studied by measuring different parameters related to an oxidative free radical challenge. Synthetic diets containing 15% (w/v) fish oil or coconut oil were used to feed growing rats for 4 weeks. As compared to control diet, the fish oil containing diet produced a significant decrease of cholesterol and triglyceride concentration in serum. however there was a significant increase in lipid peroxidation products. In addition, in fish oil fed animals, there was also a decrease in vitamin E and A concentration. Furthermore, the rate of lipid peroxidation in isolated microsomes was three fold higher in rats fed fish oil as compared to rats with coconut oil diet. No significant differences between the two experimental groups were observed in superoxide dismutase (SOD) and phospholipid hydroperoxide glutathione peroxidase (PHGPX) activities. However, there was a decrease in glutathione peroxidase (GPX) activity. These results suggest that fish oil feeding at an amount compatible with human diet, although decreasing plasma lipids, actually challenge the antioxidant defence system, thus increasing the susceptibility of tissues to free radical oxidative damage.     

Fuzzy set ordination and classification of Serengeti short grasslands,Tanzania

Abstract. Species abundance data from 32 representative stands are used to evaluate the vegetation in the heavily grazed Serengeti short grasslands. The abundant species are: Kyllinga nervosa, Sporobolus ioclados, S. kentro-phyllus and Eustachys paspaloides, all occurring in elevated areas, and Hypoestes forskalei, which is found in the drainage areas. Numerical classification and fuzzy set ordination revealed four main grassland communities associated with a topographic gradient. The communities are considered distinct since their niches, as computed in the community and environmental fuzzy system space are not overlapping. Leaching, erosion and animal disturbance effects correlated with the topographic gradient are found to determine species composition and overall community structure in the grasslands.     

A new method for characterization of N-sulfated glycosaminoglycans by a rapid and multisample nitrous acid treatment during an electrophoretic run and its application to the analysis of biological samples

A new and rapid method of nitrous acid treatment for the characterization of N-sulfated glycosaminoglycans is presented. This method permits contemporaneous nitrous acid treatment, elimination of cleavage products, and separation of other glycosaminoglycan components of biological samples during an electrophoretic run on a cellulose acetate plate.     

Reversible inactivation of a foreign gene, hph, during the asexual cycle in Neurospora crassa transformants

Summary A plasmid construct carrying the hygromycin phosphotransferase (hph) gene fused to the expression elements of the trpC gene of Aspergillus nidulans was used to obtain hygromycin B (Hyg)-resistant transformants of Neurospora crassa. The plasmid does not have any homology with the N. crassa genome. Here we demonstrate that most of the transformants arise from integration of the transforming DNA into only one of the nuclei present in the protoplasts. Furthermore, in most of the transformants the integrated transforming DNA is physically stable after growth of the transformants for about 25 nuclear divisions without Hyg selection, in spite of being present in multiple copies. In transformants carrying only a single insertion, phenotypic expression of the hph gene remains unaltered in conidial isolates obtained withoug Hyg selection. On the other hand, about 40% of transformants harbouring plasmid DNA integrated at more than one location yield conidial isolates showing reversible inactivation of the hph genes. Interestingly, the presence of methylated cytosine residues in the integrated DNA is strongly correlated with the number of plasmid copies. The hph genes are heavily methylated in transformants harbouring multiple copies but not in those harbouring only one copy of the plasmid. Phenotypic expression of the inactive hph genes can be restored by growing the transformants either under Hyg selection pressure or in the presence of 5-azacytidine. In the first case the hph genes are again inactivated when Hyg selection pressure is removed, while the activation of the hph gene by 5-azacytidine gives stable Hyg^r strains.Dedicated to Dr. T.A. Trautner on the occasion of his 60^th birthday