Glutamine synthetase (GS) expression is reduced in senile dementia of the Alzheimer type

Glutamine synthetase (GS), a metabolic marker of the mature astrocyte, was investigated in the temporal neocortex of postmortem brain samples of 8 cases, either not demented or affected by senile dementia of the Alzheimer type. A negative correlation between the GS protein level and the density of both classical A4 deposits and senile plaques was evidenced. Such a correlation for GS underlies a dysfunction of the astroglial metabolism and particularly of the glutamate and ammonia neutralization. Since GS is sensitive to oxidative lesioning, the changes in GS level that were observed, occurring at the posttranslational stage, might reflect oxidative damage and have severe consequences on the pathological cascade of events.     

Global scale patterns of fish species richness in rivers

Explanations of spatial and temporal variation in species richness is a central theme in community ecology Until recently, most research has focused on small-scale phenomena, often emphasizing on local environmental factors and, thus, poorly reflecting large-scale processes that organize species richness In this paper, we analyze variations in species richness of indigeneous freshwater fish on a worldwide scale We show that factors related to species-area and species-energy theories statistically explain most of the variation in freshwater fish species richness across continents Historical events supposed to influence present distributions offish are of little assistence in explaining variations in fish species richness at the global scale Our model, which uses easily measured factors, should also be of practical value to aquatic conservation biology and natural resource management     

Conformational change in yeast tRNAAsp

The structure of yeast tRNA^Asp in aqueous solutions has been analyzed in the light of results obtained from Raman spectra recorded at from 5 to 82°C and compared to those of tRNA^Phe. Firm evidence is given of a reversible conformation transition for tRNA^Asp at 20°C. This transition is observed for the first time in the tRNA series. The low-temperature conformation appears to have a more regular ribose–phosphate backbone and a more effective G base-stacking. This conformational change, which occurs essentially in the D loop, could be connected to the existence of two (A and B) crystal forms obtained depending on crystallization conditions. The melting temperatures, which are different for each base stacking in tRNA^Asp, lie in a range of about 70°C, much higher than for tRNA^Phe. This fact is interpreted by a higher ratio of G-C base pairs in tRNA^Asp.     

Characterization of temperate phages ofBacillus subtilis

Nine known temperature phages ofBacillus subtilis, including four that are newly isolated (ϱ6, ϱ10, ϱ14, and ϱ18), have been compared. Analysis by serology, immunity, host range, and adsorption site similarity place the phages into four groups: Group I, ϕ105, ϱ6, ϱ10, and ϱ14, which are 80–90% related; Group II, SPO2; Group III, ϕ3T and ϱ11, 100% related; and Group IV, SP16. The phage ϱ18 is largely uncharacterized, but is heteroimmune to other groups.     

Yeast transfer RNAasp: a new high-resolution x-ray diffracting crystal form of a transfer RNA.

Systematic crystallization studies on brewer's yeast aspartic acid transfer RNA have yielded different crystal forms, one of them diffracting to 3 Å resolution. The high resolution crystal form is orthorhombic ($\text{C222}{}_1\text{, a = 61}\text{A}\text{?}\text{, b = 68}\text{A}\text{?}\text{, c = 148}\text{A}\text{?}$ with one molecule per asymmetric unit) and is stable for over four days under X-rays.     

Identification of a major human serum DNA-binding protein as beta 1H of the alternative pathway of complement activation

The conformation of the molecule cyclo (Aha-$\text{Cys-Phe-D-Trp-Lys-Thr-Cys}$) was studied by empirical conformational energy calculations. The low-energy structure found contains a type II' bend centered at the D-Trp-Lys residues. The lowest energy conformer has the aromatic ring of DTrp positioned such that the γ-protons of the Lys side-chain are in the shielding region (i.e., perpendicular to the center of the aromatic ring). This is in agreement with the NMR results. A mechanism of action for the inhibition of GH release is presented which suggests a conformational change occurs in the D-Trp side-chain ring upon binding to the receptor. The resulting structure has the Phe-D-Trp ring-ring stacking suggested to be responsible for binding and agonist activity of model growth-hormone releasing peptides.     

Relationship between P700 turnover (m second) and NADP reduction as a function of ferredoxin concentration in isolated broken chloroplasts

Steady-state electron flux through P₇₀₀ (t $\text{1}\text{2}$ 20 msec) and concomitant rate of NADP reduction have been measured under weak actinic illumination as a function of concentration of ferredoxin added to broken chloroplasts isolated from peas. At suboptimal concentrations of ferredoxin this P₇₀₀ is not sufficient to account for the NADP reduction. At high concentrations ferredoxin inhibits the rate of NADP reduction without affecting the P₇₀₀ flux under short wavelength illumination. Under far red illumination P₇₀₀ flux is also inhibited by ferredoxin at high concentrations. Addition of 5 mM Mg⁺⁺ increases the rate of NADP reduction at all concentrations of ferredoxin under both kinds of illumination, while P₇₀₀ flux is inhibited under short wavelength illumination and remains unchanged under far red illumination. The results indicate that the observed (20 msec) P₇₀₀ is not involved in NADP reduction.     

A neutron investigation of yeast valyl-tRNA synthetase interaction with tRNAs.

A new way of studying RNA-protein complexes, using neutron small angle scattering in solution, is described and was applied in the case of the system, yeast valyl-tRNA synthetase, interacting with its cognate and non cognate yeast tRNAs. It was shown that, when limited amounts of tRNA (either cognate or non cognate) are added to valyl-tRNA synthetase, a complex consisting of two enzyme molecules and one tRNA molecule is first formed. It is subsequently dissociated to a one to one complex when more tRNA is present in the solution. The association curve shows a maximum for a molecular ratio, enzyme over tRNA, equal to 2.     

Produits neutres et alcaloides de Myrtopsis macrocarpa,M. myrtoidea,M. novae-caledoniae et M. sellingii

Stems and leaves of Myrtopsis macrocarpa, M. myrtoidea, M. novae-caledoniae and M. sellingii yielded terpenes, sterols, coumarins, alkaloids (furoquinolines and quinolones) and amides. A new quinolone (8-methoxy flindersine) occurs in Myrtopsis macrocarpa, a new amide (N-benzoyltryptamine) in M. myrtoidea, two new coumarins (myrsellin and myrsellinol) and a new dihydrofuroquinoline (myrtopsine) in M. sellingii. Structures of the new compounds are proposed from chemical and spectroscopic evidence.