Halobacterial megaplasmids are negatively supercoiled

Several covalently closed circular halobacterial megaplasmids (up to more than 500 kb) from different strains of Halolerax mediterranei, have been resolved by orthogonal-field alternating gel electro-phoresis (OFAGE). These molecules seem to be negatively supercoiled in vivo, as deduced from the effect of intercalating agents affecting their topology and, therefore, their electrophoretic mobility. It has also been demonstrated that the topolsomerase II Inhibitor novobiocin affects the native topological state of halobacterial megaplasmids impeding their migration in OFAGE under standard conditions for resolution of large supercoiled molecules.     

Changes in the cellular permeability of the embryonic axis inGcer arietinum L. seeds during germination

The effect of short chain fatty acids on the cellular permeability of embryonic axis inGcer arietinum seeds was studied. Octanoic (OCT) and nonanoic (NON) adds, which reduce both germination and growth of the embryonic axis and raise the inhibitor effects of the supraoptimal temperatures (30?C), induce a greater ionic efflux into the medium (conductivity). NON reduces glucose (3-0-MG) and K⁺ (⁸⁶Rb) uptake during the germinative process, this action being counteracted by fusicoccin (FC) at optimal (25?C) and supraoptimal temperatures (30 ?C). Tonoplast and plasmalemma increase their permeability to the K⁺ efflux when NON is present. Addition of NON+FC gives rise to higher values in the efflux rate, the vacuolar compartment being the most affected. Temperatures around zero (2 ?C) notably reduce the isotope efflux from cytosol and vacuole. NON acid does not significantly affect the efflux of³H-ABA, suggesting that it does not cause any important changes in the phytohormone compartmentation.     

The distribution of A1 adenosine receptor and 5′-nucleotidase in pig brain cortex subcellular fractions

Pig brain cerebral cortex was subfractionated by isopycnic centrifugation in sucrose gradients. In each subfraction the content of the agonist [³H]R-PIA binding, the activity of adenosine metabolizing enzymes (5-nucleotidase and adenosine deaminase) and the activity of membrane marker enzymes were determined. The fractions were also examined by electron microscope. In general, the results suggest a widespread distribution of A₁ adenosine receptors in membranes from different origins. Marker enzyme profile characterization indicated an enrichment of A₁ adenosine receptor in pre-synaptic membranes isolated from the crude synaptosomal fraction (P2B subfraction) as well as in membranes of glial origin such as myelin. The receptor is also present in the endoplasmic reticulum and in membranes isolated from the microsomal fraction that seem to have a post-synaptic origin (P3B). In subfractions having a high content of adenosine receptor the equilibrium binding paramters were obtained as well as the proportion of high- to low-affinity sites. From the values of the equilibrium constants it was not possible to find differences between the receptor in the different subfractions. Analysis of the affinity state distribution showed a diminished percentage of high-affinity sites in fraction P3A, which can be accounted by the existence of myelin membranes; in contrast the percentage of high-affinity states was higher in P2 and P3B, indicating that in these fractions the receptor is present in synaptosomal membranes. The close correlation shown between the enzyme 5-nucleotidase specific activity and the specific ligand binding distributions led us to postulate an important role for the enzyme in the regulation of adenosine action in pig brain cortex.     

Effect of prolactin and glucocorticoids on P-enolpyruvate carboxykinase activity in liver and mammary gland from diabetic and lactating rats

Summary The administration of 2 bromo--ergocryptine, to reduce serum prolactin decreased the activity of cytosolic P-enolpyruvatc carboxykinase (GTP) (EC4.1.1.32) about 50% in both liver and mammary gland of lactating animals. Adrenalectomy had similar effects to those of bromo-a-ergocryptine. In contrast, there was a 50% increase in enzyme activity in the mammary gland of diabetic, lactating rats and a 10-fold increase in liver as compared with normal rats. P-enolpyruvate carboxykinase activity in mammary gland as liver is coordinately regulated by prolactin, glucocorticoids and insulin.     

Muscarinic Receptor During Postnatal Development of Rat Cerebellum: An Index of Cholinergic Synapse Formation?

Abstract: Quantitative and qualitative modifications of the specific binding sites for [³H]quinuclidinyl benzylate (QNB), a muscarinic antagonist, were studied during rat cerebellar postnatal development. Specific binding sites for QNB (QNB-sbs), regardless of whether they correspond to muscarinic acetylcholine receptors, are present with the highest density in the archicerebellar cortex, but the total amount per region is about the same in the archi-, paleo-, and neocerebellar cortex regions. Large amounts of QNB-sbs are also present in a cerebellar fraction including central white matter and deep cerebellar nuclei. QNB-sbs are low but present at birth and then accumulate during ontogenic development according to a curve which duplicates, with a delay of a few days, the curve of DNA accumulation. Dissection studies indicated that this curve does not depend on the preferential localization of QNB-sbs in a specific cerebellar region nor on the particular development of this region. The similarity of the QNB-sbs and the DNA developmental curves might indicate that the QNB-sbs are present on granule cells; however, a comparative analysis of the data in the literature suggests that a great many QNB-sbs are located on the Purkinje cell dendrites in the molecular layer, where all or some of them might correspond to the ex-trajunctional muscarinic acetylcholine receptor detected there by electrophysiology. It would appear that only a small percentage of cerebellar QNB-sbs corresponds to the cholinergic synapses present in cerebellar cortex; hence, the question of muscarinic receptors in the cerebellum should be re-examined.     

A possible specific receptor for 3-beta-androstanediol in the human sebaceous gland

Dihydrotestosterone (DHT) does not seem to be the active specific metabolite of testosterone in hypertrophic sebaceous glands of subjects affected by male pattern baldness (MPB) and several results indicate that probably 3-beta-androstanediol (beta DIOL) could be an active form of testosterone in those glands. Cytosol and serum from several patients affected by MPB and subjected to hair autotransplantation, was incubated with both beta DIOL and 3-alpha-androstanediol (alpha DIOL). Binding patterns indicate that alpha DIOL binds to cytosolic proteins probably due to the contaminating sex hormone binding globulin (SHBG), whereas beta DIOL exhibits an atypical binding process in cytosol in the presence of high concentrations of non radioactive beta DIOL. This binding increases progressively up to 2 pmol/mg protein at the limit solubility conditions for the non radioactive steroid. This pattern is not observed in serum from the same patients, where the binding of beta DIOL is typically restricted to the SHBG. These results strongly suggest the existence of a specific beta DIOL-binding protein in the hypertrophic sebaceous glands and explain the lack of specific receptor for DHT in these tissues.     

Theoretical study of the acidic strength of amino acid side chains

The acidic strengths in gas phase of three groups (NH₄⁺, H₂S, and HCOOH) that mimic the most common amino acid side chains of enzymes are studied by means of quantum mechanical methods. The results demonstrate that in gas phase the acidities of such groups change drastically with respect to those reported in aqueous phase. Moreover, the dependence between the energetics of the proton-transfer process and the distance separating the acid and base groups is stated. The biological implications of these results are discussed.     

Magic angle spinning 13C-NMR spin-lattice relaxation study of the location and effects of α-tocopherol,ubiquinone-10 and ubiquinol-10 in unsonicated model membranes

-Tocopherol, ubiquinone-10 and ubiquinol-10 have been studied by high resolution magic angle samples spinning ¹³C-nuclear magnetic resonance in egg yolk phosphatidylcholine multilamellar vesicles model membranes in order to assess their location and the induced perturbations on this model system. -Tocopherol is placed in such a position that it is in close contact with the head group of the phospholipid and exposed to the solvent. In this position it significantly perturbs the phospholipid head group, the 5a-CH₃ and the 7a-CH₃ groups being the closest parts to the membrane surface. On the other hand, ubiquinol-10 perturbs the membrane surface more than ubiquinone-10, but neither compound significantly changed the phospholipid head group conformation.     

Induced spawning by LHRHa and pimozide in the Asian catfish Clarias macrocephalus (Gunther)

Experiments were conducted to determine the optimum dose of luteinizing hormone-releasing hormone analogue (LHRHa) and pimozide (PIM) injected simultaneously to yield a high ovulation rate and produce sufficient eggs in the Asian catfish Clarias macrocephalus . In June 1990, injection of 0.05 or 0.10 μg LHRHa/g body weight (BW) + 1 μg PIM/g resulted in 100% ovulation, while only 80% of gravid catfish injected 0.025 μg LHRHa + 1 μg PIM/g ovulated. Most of the eggs stripped from 6 out of 8 control fish were not mature. Fertilization and hatching rates of LHRHa + PIM-induced fish (75–90% and 39–51%, respectively) were higher than those of control fish (36–39% and 0–1% respectively). In August and September 1990, at gravid catfish ovulated after injection of 0.05–0.10 μg LHRHa + 1 μg PIM/g BW. However, only 20% of the fish given 0.025 μg LHRHa/g + 1 μg PIM/g BW in August ovulated. No eggs could be striped from any of the control fish in August and September 1990. Techniques developed in this study, showed a simple and effective way of spawning captive catfish, C. macrocephalus . A simultaneous intramuscular injection of 0.05 μg LHRHa + 1 μg PIM/g and stripping of eggs at 16–20 h post-injection have been tested to yield high ovulation, fertilization and hatching rates.