Measurements of conformational changes during adhesion of lipid and protein (polylysine and S-layer) surfaces

The adhesion forces between various surfaces were measured using the "surface forces apparatus" technique. This technique allows for the thickness of surface layers and the adhesion force between them to be directly measured in controlled vapor or liquid environments. Three types of biological surfaces were prepared by depositing various lipid-protein monolayers (with thicknesses ranging from 1 to 4 nm) on the inert, molecularly smooth mica surface: (i) hydrophobic lipid monolayers; (ii) amphiphilic polyelectrolyte surfaces of adsorbed polylysine; and (iii) deposited bacterial S-layer proteins. The adhesion, swelling, and wetting properties of these surfaces was measured as a function of relative humidity and time. Initial adhesion is due mainly to the van der Waals forces arising from nonpolar (hydrophobic) contacts. Following adhesive contact, significant molecular rearrangements can occur which alter their hydrophobic-hydrophilic balance and increase their adhesion with time. Increased adhesion is generally enhanced by (i) increased relative humidity (or degree of hydration); (ii) increased contact time; and (iii) increased rates of separation. The results are likely to be applicable to the adhesion of many other biosurfaces, and show that the hydrophobicity of a lipid or protein surface is not an intrinsic property of that surface but depends on its environment (e.g., on whether it is in aqueous solution or exposed to the atmosphere), and on the relative humidity of the atmosphere. It also depends on whether the surface is in adhesive contact with another surface and-when considering dynamic (nonequilibrium) conditions-on the time and previous history of its interaction with that surface. (c) 1993 John Wiley & Sons, Inc.     

Effects of bile salt infusion on chlorpromazine-induced cholestasis in the isolated perfused rat liver.

The present study has demonstrated that tauroursodeoxycholate (TUDC), but not taurocholate, can reverse chlorpromazine (CPZ)-induced cholestasis in the isolated perfused rat liver. At an infusion rate of 1.5 mumol/min, TUDC led to restoration of bile flow in the perfused rat liver made cholestatic by the addition of 250 microM CPZ. This reversal was accompanied by an increased excretion of CPZ and its metabolites. A higher infusion rate of 5.0 mumols TUDC/min, however, led to only a transient increase in bile flow and to no increase in CPZ excretion. In contrast to the effects of TUDC, infusion of taurocholate led to an exacerbation of CPZ-induced cholestasis. The differences in the efficacy of the two bile salts may be due to their relative detergent (hydrophobic) properties.     

Evidence for the presence of β-lactamase inStreptomyces glaucescens and its inhibition by sodium clavulanate

Streptomyces glaucescens is shown to possess -lactamase activity which is inhibitable by clavulanate. This is important in regard to its use as a cloning host for enzymes of \-lactam biosynthesis.     

Geochemical partitioning and bioavailability of copper to aquatic plants in an artificial oxide-organic sediment

This study investigated the effects of competition between binding substrates (organic matter and iron oxide) and between metals (cadmium and copper), on the partitioning of sedimentary copper and its subsequent bioavailability to an aquatic plant. Organic matter and a synthesized iron oxide, ferrihydrite, were added singly and in combination to a series of sand sediments, which were then dosed with environmentally realistic concentrations of cadmium and copper and planted with rice,Oryza sativa. Organic matter controlled copper partitioning and bioavailability, whereas the synthetic ferrihydrite bound negligible amounts of either metal, even in the absence of organic matter. As organic matter concentrations increased, operationally-defined leachable copper decreased, organic-associated copper increased and the survival of rice plants improved in an approximately linear fashion. At a nominal starting copper concentration of 5.8 μg g dry wt⁻¹, plant survival after four weeks averaged 0–8% in sediments without organic matter, 25% in a sediment containing 0.18% organic matter and 58% in a sediment containing 0.36% organic matter. These results suggest that organic-associated forms of copper are unavailable to plants, and that the operational definition of ‘leachable’ copper (extracted with dilute ammonium acetate) adequately represents the species of copper that is (are) available to plants. Our study using a well-characterized artificial sediment supports the copper fractionation patterns and correlations between copper partitioning and bioavailability reported from the heterogeneous, poorly characterized sediments of natural lake and river sediments.     

Vasopressinergic and oxytocinergic pathways in the central nervous system

Recent data obtained by immunohistochemical and other anatomical tracing methods indicate that oxytocin and vasopressin pathways are much more complex and extensive than previously recognized. In addition to the classic magnocellular neurons that project from the supraoptic and paraventricular (PVN) nuclei to the posterior pituitary gland, generally smaller neurons in various parts of the PVN send vasopressin fibers to the portal capillary bed in the median eminence, or send oxytocin or vasopressin projections to other brain and spinal cord sites. In addition, vasopressin neurons are also found in the suprachiasmatic nucleus and may contribute to extrahypothalamic projection areas. Many of these axonal projections appear to form synapses with other neurons in forebrain, hindbrain, and spinal cord regions, which suggests roles for these peptides in neuronal communication. In brain stem and spinal cord, terminal fields include both parasympathetic and sympathetic regulatory centers. Oxytocin terminals are also found on large intracerebral arteries where the peptide may regulate cerebral blood flow.     

Rooting apple cultivars in vitro: Interactions among light,temperature, phloroglucinol and auxin

Delicious apple (Malus domestica Borkh.) and several of its strains, which have been difficult to root in vitro, were successfully propagated with rooting percentages up to 100%. The combination of treatments used to achieve this result included placing the shoots on rooting medium in the dark at 30°C for the first week of the rooting stage, then moving them to a regime of 16 hr light-8 hr dark at 25°C. The rooting medium contained half strength Murashige and Skoog salts plus 1.2 M thiamine HCl, 0.56 mM myo-inositol, 1 mM phloroglucinol (PG), 1.4 M indolebutyric acid (IBA), 1.3 M gibberellic acid (GA₃), 87.6 mM sucrose, and 7 g l^–1 Difco Bacto agar. Dark treatment applied during the proliferation stage (etiolation) was less effective than one applied at the beginning of the rooting stage. The optimum length of dark treatment during rooting was 4 to 7 days. Increasing the temperature from 25°C to 30°C improved rooting of Delicious, Royal Red Delicious, and Vermont Spur Delicious in the absence of PG but generally had less effect in the presence of PG. Further increase in temperature to 35°C stimulated rooting of Royal Red Delicious but reduced rooting of Vermont Spur Delicious. Transfer of the cuttings to auxin-free medium after 1 week had no effect on percentage rooting and increased the number of roots per cutting for only 1 of 4 cultivars tested and then only in the presence of PG. In general PG stimulated rooting of Delicious and its strains, but had no effect on Golden Delicious.     

Cyanophycin granule polypeptide protease in a unicellular cyanobacterium

An assay was developed to measure the proteolysis of cyanophycin granule polypeptide in crude extracts of a unicellular cyanobacterium. The substrate was radioactively labeled cyanophycin granule polypeptide formed by an unicellular cyanobacterium grown in the presence of chloramphenicol. Substrate polypeptide displayed identical chemical properties with polypeptide isolated from non-chloramphenicol-treated cells. Solubilization of radioactivity as arginine indicated hydrolysis of polypeptide. Radioactively labeled aspartate and arginine from hydrolyzed polypeptide was related to nmol amino acid using a combination of paper chromatography, liquid scintillation analysis, and ninhydrin quantitation. Protease activity was found in extracts of nitrogen-limited cells harvested 16–24 h after a nitrogen source was added back. Optimal pH for protease activity was 8.0 and optimum temperature was 35°C. Protease activity in crude extracts followed Michaelis-Menten kinetics with a V _max of 92 nmol arginine per 15 min/mg protein and a K _m of 2.1×10³ nmol arginine. Protease activity was inhibited by arginine and by high concentrations of aspartate.