Inhibition of early steps of de novo fatty-acid biosynthesis by different xenobiotica

The importance of the early steps of de novo fatty-acid biosynthesis is discussed in terms of rate-limiting enzymic reactions with respect to their inhibition by xenobiotics. The inhibitory spectra of allicin as an inhibitor of the acetyl-CoA-synthase, two classes of graminicides (cyclohexane-1,3-diones and aryloxyphenoxypropionic acids) as inhibitors of acetyl-CoA-carboxylase, and the two antibiotics cerulenin and thiolactomycin, which affect the condensing step in fatty-acid biosynthesis, are compared.     

Armaments and ornaments: an evolutionary explanation of traits of dual Utility

Secondary sexual characters in many species function both in male-male competition and as cues for female choice. Based on a literature compilation of existing knowledge of traits with this dual function, we propose that they commonly arise through intersexual selection processes and serve as honest signals to other males regarding fighting ability or dominance. Faking these traits, here called armaments, (i.e. weapons and status badges) is difficult, as they are constantly put to trial in male-male contests. Females that subsequently utilize them as indicators of male phenotypic quality when selecting a partner will benefit by acquiring males of higher quality to father their offspring. Thus, evolution of armaments through male-male competition is seen as a usually initiating process, whereas female choice later may assume a role as an additional selective factor. The reverse, that males use information from traits evolved through female choice, is, however, also possible. The traditional view of independently evolved and temporarily unordered intra- and intersexual selection processes fails to explain dual trait functions. Moreover, our model may more satisfyingly than traditional ones explain how trait honesty and trait genetic variance are maintained: theoretical and empirical evidence suggests that such honesty and variation are more easily maintained under male-male competition than under female choice.     

Evidence for the Existence of Differential O-Glycosylated α5-Subunits of the γ-Aminobutyric AcidA Receptor in the Rat Brain

Abstract: Polyclonal antibodies were raised to synthetic peptides having amino acid sequences corresponding with the N- or C-terminal part of the γ-aminobutyric acid_A (GABA_A) receptor α₅-subunit. These anti-peptide α₅(2–10) or anti-peptide α₅(427–433) antibodies reacted specifically with GABA_A receptors purified from the brains of 5–10-day-old rats in an enzyme-linked immunosorbent assay and were able to dose-dependently immunoprecipitate up to 6.3 or 13.1% of the GABA_A receptors present in the incubation, respectively. In immunoblots, each of these antibodies reacted with the same two protein bands with apparent molecular mass of 53 or 57 kDa. After exhaustive treatment of purified GABA_A receptors with N -Glycanase, each of these antibodies identified two proteins with apparent molecular masses of 46 and 48 kDa. Additional treatment of GABA_A receptors with neuraminidase and O -Glycanase resulted in an apparently single protein with molecular mass of 47 kDa, which again was identified by both the anti-peptide α₅(2–10) and the anti-peptide α₅(427–433) antibody. These results indicate the existence of at least two different α₅-sub-units of the GABA_A receptor that differ in their carbohydrate content. In contrast to other α- or β-subunits of GABA_A receptors so far investigated, at least one of these two α₅-subunits contains O-linked carbohydrates.     

Molecular cloning and functional expression of bacteriophage PK1E-encoded endoneuraminidase Endo NE

Homopolymeric α-2,8-linked sialic acid (PSA) has been found as a capsular component of sepsis- and meningitis-causing bacterial pathogens, and on eukaryotic cells as a post-translational modification of the neural cell adhesion molecule (NCAM). The polysaccharide is specifically recognized and degraded by a phage-encoded enzyme, the endo-N-acetylneuraminidase E (Endo NE). Endo NE therefore has become a valuable tool in the study of bacterial pathogenesis and eukaryotic morphogenesis. In this report we describe the molecular cloning of Endo NE and the expression of a functionally active recombinant enzyme. The cloned DNA sequence (2436 bp) encodes a polypeptide of 811 amino acids, which at the 5′ end contains a totally conserved neuraminidase motif. Expressed in Escherichia coli, the enzyme migrates as a single band of approximately 74 kDa in SDS-PAGE. A central domain of 669 amino acid residues is about 90% homologous to the recently cloned Endo NF. Both phage-induced lysis of bacteria and the catalysis of PSA degradation by the recombinant enzyme are efficiently inhibited by a polyclonal antiserum raised against the intact phage particle. The C-terminal region seems to be essential to enzymatic functions, as truncation of 32 amino acids outside the homology domain completely abolishes Endo NE activity. Our data also indicate that the 38 kDa protein, previously assumed to be a subunit of the Endo NE holoenzyme, is the product of a separate gene locus and is not necessary for in vitro depolymerase activity.     

Uptake and Storage of Choline by Rat Brain: Influence of Dietary Choline Supplementation

In order to elucidate the regulation of the levels of free choline in the brain, we investigated the influence of chronic and acute choline administration on choline levels in blood, CSF, and brain of the rat and on net movements of choline into and out of the brain as calculated from the arteriovenous differences of choline across the brain. Dietary choline supplementation led to an increase in plasma choline levels of 50% and to an increase in the net release of choline from the brain as compared to a matched group of animals which were kept on a standard diet and exhibited identical arterial plasma levels. Moreover, the choline concentration in the CSF and brain tissue was doubled. In the same rats, the injection of 60 mg/kg choline chloride did not lead to an additional increase of the brain choline levels, whereas in control animals choline injection caused a significant increase; however, this increase in no case surpassed the levels caused by chronic choline supplementation. The net uptake of choline after acute choline administration was strongly reduced in the high-choline group (from 418 to 158 nmol/g). Both diet groups metabolized the bulk (greater than 96%) of newly taken up choline rapidly. The results indicate that choline supplementation markedly attenuates the rise of free choline in the brain that is observed after acute choline administration. The rapid metabolic choline clearance was not reduced by dietary choline load. We conclude that the brain is protected from excess choline by rapid metabolism, as well as by adaptive, diet-induced changes of the net uptake and release of choline.     

Regional Amino Acid Distribution in Relation to Function in Insulin Hypoglycaemia

The amino acids glutamate, aspartate, gamma-aminobutyric acid (GABA), and glutamine were measured as their dansyl derivatives in whole brain and specific brain regions by a sensitive double-labelling technique at various times during the development of hypoglycaemic encephalopathy. Hypoglycaemia was induced by administration of insulin (100 i.u./kg) to 24-h fasted rats. No significant changes in glutamate, GABA, or glutamine were detected in whole brain at any time up to and including the onset of hypoglycaemic convulsions. In cerebral cortex, however, GABA levels were reduced to 65% or normal prior to the appearance of neurological symptoms of hypoglycaemia. Onset of symptoms (severe catalepsy and loss of righting reflex, but before the onset of convulsions) was accompanied by marked decreases of glutamate and glutamine in striatum and hippocampus. These regions, in addition to cerebral cortex, show the greatest vulnerability to hypoglycaemic insult, according to previous anatomical studies. Aspartate levels were significantly increased (p less than 0.01) in the cerebral cortex of convulsing animals, confirming a previous report. No changes were detectable in any of the amino acids studied in medulla-pons at any time during the progression of hypoglycaemia. Cerebral cortex and striatum showed a selective net loss of amino acids (2.2 and 3.5 mumol/g. respectively) prior to the onset of insulin-hypoglycaemic convulsions.     

Maintenance of labour.

In 160 women large but variable amounts of intravenous oxytocin were needed to induce labour within a reasonable time interval to 5 cm cervical dilatation. Thereafter 7 mU of oxytocin/min would maintain progress. Since large maintenance doses may cause obstetric problems it is recommended that a maintenance regimen should be used once labour has progressed to this stage.     

Spreading of human fibroblasts in serum-free medium: Inhibition by dithiothreitol and the effect of cold insoluble globulin (plasma fibronectin)

We have tested the effect of dithiothreitol (DTT) treatment on the initial spreading of human fibroblasts in serum-free medium in tissue culture dishes. Cell spreading was inhibited following treatment of these cells with 10 mM DTT. Inhibition occurred when the cells were treated at 37°C but not at 4° and was reversible metabolically but not by the addition of sulfhydryl oxidizing reagents. The inhibition was overcome when DTT-treated human fibroblasts were plated on cold insoluble globulin (plasma fibronectin)—coated dishes. Under these conditions spreading appeared to be completely normal, including the formation of focal adhesions. Analysis of the fibronectin concentrations in the human fibroblasts following DTT treatment indicated that there was little decrease in the absolute level of activity as determined in a biological assay for BHK cell spreading on culture dishes. Analysis of the fibronectin distribution on the DTT-treated human fibroblasts by indirect immunofluorescence using a specific anti-CIG antiserum revealed that fibronectin was no longer deposited onto the culture dish surfaces. Even when the DTT-treated human fibroblasts spread in the presence of fetal calf serum, the cell fibronectin remained for the most part in a perinuclear location. These results indicate that DTT treatment of human fibroblasts prevents the normal translocation of fibronectin from a perinuclear location to the surface of the culture dish. This study further supports our hypothesis that the initial spreading in serum-free medium of fibroblasts from cell strains depends upon secretion of fibronectin onto the culture dish surface.