Conflicting evidence regarding the transport of alpha-glutamyl-dipeptides by human erythrocytes.

A novel ninhydrin-positive compound, N-methyl-D-aspartic acid, was identified in the muscle extracts of the blood shell, Scapharca broughtonii. This compound is already known to have potent neuroexcitatory activity, inducing hypermotility and strong releasing action of serum luteinizing hormone in mammals. This may be, however, the first finding of N-methyl-D-aspartic acid in natural products.     

Paleoceanographic interpretations of coccoliths and oxygen-isotopes from the sediment surface of the southwest Indian Ocean

The distribution of forty-four coccolithophore species in one hundred deep-sea core-tops from the southwest Indian Ocean is described. Three coccolith assemblages have been recognised (Maputo, Agulhas Current and deep water) by the relative abundances of four ecologically significant coccolithophore species (Gephyrocapsa oceanica, Emiliania huxleyi, Calcidiscus leptoporus and Umbilicosphaera sibogae). Their biogeographical distribution appears to be related to water temperature, nutrient concentration and dissolution.The degree of preservation of coccoliths and foraminifera indicates that the carbonate lysocline lies somewhere between 3500 and 4000 m, resulting in the concentration of dissolution-resistant microfossils below this depth.Stable oxygen isotope ratios of the planktonic foraminiferal species Globigerinoides sacculifer range between −1.5 to −1.0‰ PDB (equal to 22.8–25.1°C) and occur in a narrow band on the sea floor beneath the “A” route of the Agulhas Current.These values are about 0.5 per mil PDB lighter than samples analyzed on either side of this band and can be explained by the Agulhas Current's elevated temperature at the ocean surface of 2–3°C. Thus an oxygen isotope imprint of the Agulhas Current exists beneath it on the sea floor.The Agulhas Current is probably the major factor influencing sedimentation, sediment-distribution patterns and geological features in the study area. At present it is voluminous and fast flowing, possibly eroding sediments up to 2500 m below the surface.The oxygen-isotope ratios and nannoplankton counts obtained in this study indicate, however, that the majority of samples are most probably recent or at least not older than 85,000 years. This implies that sediments are accumulating on the ocean floor and that the Agulhas Current does not have a pronounced erosional influence, at least in areas from which cores were retrieved for this study.     

Molecular organisation of the malate synthase genes of Aspergillus nidulans and Neurospora crassa

Summary A soybean nodulin cDNA clone (E41) hybrid-selected mRNA for three in vitro translation products with apparent molecular weights of 26 kDa, 25 kDa and 24 kDa. Based on Southern analysis of soybean genomic DNA, combined with mapping and sequencing of genomic clones, we identified four genes that are related to E41, one of which was identified to be the previously characterized N-20 gene. Our data indicate the linkage of three of the genes, of which one is a truncated version and suggest that they originated by gene duplication combined with deletion and conversion. The genes are highly expressed and we postulate that the sequence conservation in the 5 and 3 flanking regions of all four genes, has a functional role in their expression. Hybrid-selected translation products of E41 are not immunoprecipitable with antibody to the soluble fraction of nodules suggesting that they are membrane associated. The N-20 gene, which is a member of this gene subfamily, showed sequence similarity to four previously characterized nodulin genes and a phylogenetic tree is proposed based on the extent of sequence similarity.     

The influence of fish oil supplementation on plasma lipoproteins and arterial lipids in vervet monkeys with established atherosclerosis.

There is controversy about whether supplementing diets with marine fish oil can regress, promote or prevent atherosclerosis. Therefore the effects of an Atlantic pilchard oil (FO) supplement and dietary change were measured in a proven atherosclerosis model. Vervet or African Green monkeys were fed an atherogenic diet (AD) for long enough to ensure progression before treatments started. Matched groups were then treated for 20 months, either by adding FO to the AD (AD/FO), or by changing to a therapeutic diet with FO (TD/FO). Control treatments consisted of supplementing with sunflower oil (SO) instead of FO, so that treatments were AD/SO and TD/SO. The same total polyunsaturates were supplied by the FO and SO and the dose of FO was realistic (2.5% of total energy). A reference group (R) received the TD with no oil supplements. Supplementing with FO did not change the concentrations of total, low or high density lipoprotein cholesterol in plasma. After The AD/FO the intimas of aortas contained more total (p < or = 0.001), free (p < or = 0.05) and esterified (p < or = 0.05) cholesterol, total phospholipid (p < or = 0.01) and sphingomyelin (p < or = 0.05) than after the AD/SO. After FO supplementation eicosapentaenoic acid was significantly higher and arachidonic acid significantly lower in the plasma and aorta intima phosphatidylcholine. None of these changes was anti-atherogenic in terms of atherosclerosis measured in the same individuals (1). Nor did FO increase the efficacy of the TD.     

Sequencing Studies of Icr-170 Mutagenic Specificity in the am (Nadp-Specific Glutamate Dehydrogenase) Gene of NEUROSPORA CRASSA

The acridine half-mustard ICR-170-induced reversion of the mutant am15, which has a single base-pair deletion, at a frequency of between 9 and 28 X 10(-6). In each of three classes of revertants, the mutagen had induced the insertion of a -G- -C- base pair at a -G-G- -C-C- site. The mutant am6, which has a single base pair insertion, is known to be revertible, with UV light, by deletion of a -G- -C- base pair at a -G-G-G- -C-C-C- site. This mutant reverted with ICR-170 at a frequency of 0.1 X 10(-6). These results show that ICR-170 is able to induce addition frameshifts in Neurospora crassa within short, monotonous runs of G:C base pairs, but indicate a lack of deletion activity at such sequences.     

Nature of the Complementation Products Formed by a Complementing Mutant of Neurospora crassa

The mutant am-14 produces no active nicotinamide adenine dinucleotide phosphate-linked glutamate dehydrogenase (GDH) and no protein showing immunological cross-reaction with the enzyme. Nevertheless, it shows complementation with several other am mutants in heterokaryons. Active GDH can be extracted from heterokaryons formed from am-14 and other mutants which, by themselves, produce more or less inactive varieties of the enzyme. The enzyme from am-14 + am-3 heterokaryons can be partially separated from am-3 mutant GDH on a diethylaminoethyl cellulose column. It is characterized by abnormally high thermolability and by a capacity for activation by glutamate. By the same procedure as brings about hybridization between mutant GDH proteins, it has been possible to recover enzyme with the properties of pure am-3 GDH from a partially purified am-14 + am-3 GDH preparation which was initially substantially free of unhybridized am-3 enzyme. This is interpreted as evidence that the active complementation product is a hybrid oligomer containing am-3 monomers and also am-14 monomers, the latter being unable to aggregate by themselves. Heterokaryons formed from am-14 and wild type produce GDH of abnormally high thermolability, presumably due to the formation of am-14 + am(+) hybrids.     

Detection of monodisperse aggregates of a recombinant amelogenin by dynamic light scattering

Recombinant murine amelogenins M179 and M166 were expressed in Escherichia coli and purified. The aggregation properties of these amelogenins have been investigated in aqueous solutions as well as acetonitrile-containing solutions using dynamic light scattering. Dynamic light scattering provides direct measurement of the translational diffusion coefficient and hydrodynamic radius, and of an estimate of the molecular weight. Polydispersity and statistical parameters of how to interpret the analysis are also provided. Amelogenin aggregation was examined in solutions of a range of pH, ionic strengths, and protein concentrations. It was shown that at pH 7.8–8 and ionic strength of 0.02–0.05M the M179 molecules form monodispersed aggregates with hydrodynamic radii ranging from 15 to 19 nm. Analysis of hydrodynamic radii and size distribution of M179 aggregates in acetonitrile-containing solvents compared to that in aqueous solutions indicated a primary role for hydrophobic interactions in the association process of amelogenin molecules to form aggregates. Comparison between the aggregates formed by M179 and M166, which lacks the hydrophilic carboxy-terminal 13 residue sequence of M179, suggested that the self-assembly of amelogenin molecules to form stable and monodisperse aggregates requires the presence of the hydrophilic carboxy-terminal sequence of M179. © 1994 John Wiley & Sons, Inc.     

How many additional parameters in a conversion model can be evaluated using "corresponding-site" events?

Contrary to a recent claim by B.C. Lamb and S.A. Zwolinski (1992), the frequencies of "corresponding-site" conversion events (all four chromatids involved in conversion at the same locus in the same meiotic cell) can be used to evaluate only two parameters not otherwise calculable: a coincidence parameter and the frequency of conversion-type events in which a normal 1:1 ratio is restored.     

Separation of v-Src-induced mitogenesis and morphological transformation by inhibition of AP-1.

v-Src activity results in both morphological transformation and reentry of quiescent chick embryo fibroblasts (CEF) into cell cycle. We have previously used temperature-sensitive v-Src mutants to show that enhanced activity of cellular AP-1 in the first few hours after activation of v-Src invariably precedes the biological consequences. Here we have investigated whether the early activation of AP-1 is essential for any or all of the v-Src responses by using a mutant c-Fos that comprises the leucine zipper and a disrupted basic region. Expression of the c-Fos mutant partially reduced cellular AP-1 activity in exponentially growing cells. However, in CEF that had been made quiescent by serum deprivation, v-Src-induced stimulation of AP-1 DNA binding activity was substantially reduced. In addition, quiescent CEF stably transfected with this mutant show an impaired mitogenic response to v-Src, indicating that the AP-1 stimulation is a necessary prerequisite for cell-cycle reentry. The ability of v-Src to morphologically transform quiescent CEF was not impaired by the inhibition of AP-1 stimulation, indicating that the mitogenic and morphological consequences of v-Src have distinguishable biochemical mediators. Focal adhesion kinase, a recently identified determinant of cell morphology, undergoes a gel mobility shift, characteristic of its hyperphosphorylated state, in response to v-Src activation in cells expressing the inhibitory AP-1 protein. This provides further evidence that the pathways that regulate morphological transformation are independent of AP-1.     

Synthesis and biological evaluation of novel NK-1 tachykinin receptor antagonists: The use of cycloalkyl amino acids as a template

In the course of a program aimed at synthesizing novel, potent NK-1 tachykinin receptor antagonists, we developed upon a bioactive model by comparing the low energy structures of a series of peptide and nonpeptide Substance P antagonists. The comparison was based on the super imposition of the aromatic rings, assuming that the rest of the molecule behaves predominantly as a template to arrange the key aromatic groups in the right spatial position. A series of 2-aminocyclohexane carboxylic acid analogues were then selected as the best templates for reproducing the postulated bioactive structure, leading to several pseudo-peptides with interesting biological activity. According to the molecular modeling, these compounds exhibit a neat parallel facing of the indolyl and naphthyl groups at about 3 Å distance. Ultraviolet absorption and steady state fluorescence measurements support this conclusion, showing a linear correlation between the spectral properties and the binding affinity of these analogues. Stacking of the indole ring with naphthalene gives rise to a complex characterized by a well-defined molar extinction coefficient. Consistently, steady state and lifetime fluorescence measurements suggest that the quenching process is ascribable to ground-state interactions between the chromophores. Implications of the π stacking propensity of aromatic groups in the biological activity of the compounds examined are briefly discussed. © 1995 John Wiley & Sons, Inc.