Malondialdehyde production from spermine by homogenates of normal and transformed cells

The oxidation of spermine in vitro by a mixture of polyamine oxidase and diamine oxidase from pig kidney gives rise to malondialdehyde via 3-aminopropanol as the intermediate. Conversely, with spermidine, under similar experimental conditions, no evidence could be obtained for malondialdehyde formation within the limits of sensitivity of the assay (2.0 nmol). The activities of both these enzymes show about a 2-fold increase in normal rat kidney cells (LA31 NRK) transformed by the temperature sensitive mutant of Rous sarcoma virus (LA31) and incubated at the non permissive temperature (39 degrees C) compared to the activities in LA31 NRK at the permissive temperature (33 degrees C). These same enzymatic activities show no temperature dependent changes in normal rat kidney cells (NRK) or in these same cells infected by the wild type virus (NRK B77). In extracts derived from Friend erythroleukemic cells induced to differentiate by dimethyl sulfoxide or hexamethylene bis acetamide, spermine oxidation takes place more efficiently than in non induced cells. A rise in diamine oxidase activity is seen in LA31 NRK (39 degrees C) 12 h after the temperature shift, whereas morphological manifestations of normalcy are seen only at 48 h. The Km of diamine oxidase is 10(-6) M for putrescine and 10(-3) M for 3-aminopropanol. A possible mechanism involving the well documented acetylation of putrescine [23,26] is proposed for diverting intracellular putrescine away from cytosolic diamine oxidase and towards intramitochondrial monoamine oxidase.     

Immunolocalization of parvalbumin in two glutamatergic cell types of the guinea pig cochlea: inner hair cells and spinal ganglion neurons

Immunoreactions to a monoclonal antibody raised against parvalbumin, a calcium-binding protein, have been detected in the inner hair cells of the organ of Corti and in the spiral ganglion neurons connected to them (type I neurons). Both cell types probably use an excitatory amino acid as a neurotransmitter (glutamate and/or aspartate). No immunoreactivity was found within the second sensory cell type (outer hair cells) nor in the olivocochlear (efferent) fibers or endings in the cochlea. In the central nervous system, parvalbumin may be involved in calcium-dependent mechanisms leading to neurotransmitter release. It could thus be hypothesized that parvalbumin also have similar implications at the level of the inner hair cell and type I neuron synapses. Additional functions could also be hypothesized for this protein in the cochlea. Within the inner hair cells, parvalbumin may be involved in the ionic regulation following potassium entry during the transduction process. Within type I neurons, by buffering sudden increases in the intracellular calcium concentration, it may allow an adaptation of the firing rate to variations in the intensity of sound stimuli.     

DETERMINATION OF GUSTATORY SUCROSE THRESHOLD IN WATER BY USE OF A LINEAR SUCROSE GRADIENT

A novel experimental method was developed which allows the determination of the threshold concentration of sucrose by use of a linear sucrose gradient in water. With this method a continuous tasting of the test-liquid is possible. A panel of 15 persons experienced in taste-testing was used. Three gradients of different steepness were applied: 0 to 1.5% (w/w) sucrose in 2 min (I), 3 min (II) and 4 min (III). The results of the new method were compared with those of the standard method (DIN). With gradients I and II we found values which were significantly higher than those of the standard method (I: 0.49% (w/w); II: 0.46% (w/w); DIN: 0.31% (w/w)), whereas with gradient III the same threshold value was found as with the DIN-Method (III: 0.32% (w/w)).     

Conformational stability of a thrombin-binding peptide derived from the hirudin C-terminus.

The COOH-terminal region of hirudin represents an independent functional domain that binds to an anion-binding exosite of thrombin and inhibits the interaction of thrombin with fibrinogen and regulatory proteins in blood coagulation. The thrombin-bound structure of the peptide fragment, hirudin 55-65, has been determined by use of transferred NOE spectroscopy [Ni, F., Konishi, Y., & Scheraga, H. A. (1990) Biochemistry 29, 4479-4489]. The stability of the thrombin-bound conformation has been characterized further by a combined NMR and theoretical analysis of the conformational ensemble accessible by the hirudin peptide. Medium- and long-range NOE's were found for the free hirudin peptide in aqueous solution and in a mixture of dimethyl sulfoxide and water at both ambient (25 degrees C) and low (0 degrees C) temperatures, suggesting that ordered conformations are highly populated in solution. The global folding of these conformations is similar to that in the thrombin-bound state, as indicated by NOE's involving the side-chain protons of residues Phe(56), Ile(59), Pro(60), Tyr(63), and Leu(64). Residues Glu(61), Glu(62), Tyr(63), and Leu(64) all contain approximately 50% of helical conformations calculated from the ratio of the sequential dNN and d alpha N NOE's. Among the helical ensemble, active 3(10)-helical conformations were found by an analysis of the medium-range [(i,i+2) and (i,i+3)] NOE's involving the last six residues of the peptide. An analysis of the side-chain rotamers revealed that, upon binding to thrombin, there may be a rotation around the alpha CH-beta CH bond of Ile(59) such that Ile(59) adopts a gauche- (chi 1 = +60) conformation in contrast to the highly populated trans (chi 1 = -60) found for Ile(59) in the free peptide. However, the thrombin-bound conformation of the hirudin peptide is still an intrinsically stable conformer, and the preferred conformational ensemble of the peptide contains a large population of the active conformation. The apparent preference for a gauche- (chi 1 = +60) side-chain conformation of Ile(59) in the bound state may be explained by the existence of a positively charged arginine residue among the hydrophobic residues in the thrombin exosite.     

A procedure for the extraction of chloroplast DNA from broad-leaved tree species

A method for the extraction of ctDNA from isolated chloroplast was developed. This method is simple and adapted particularly to broad-leaved trees, including sclerophyllous species with high phenolic and polysaccharide contents. This method includes two major steps: first, chloroplasts are isolated in non-aqueous solutions to avoid oxidation and phenolic problems; second, ctDNA is extracted from the chloroplasts using aqueous solutions and specific methods to provide highly purified ctDNA.     

Effect of neurotensin on pancreatic function in man

The effect of neurotensin on submaximally-stimulated hepatobiliary and pancreatic secretion was studied in 6 healthy subjects. An intravenous infusion of neurotensin 1.4 ± 0.3 pmol/kg/min, designed to reproduce plasma neurotensin immunoreactivity levels within the physiological range, produced a significant increase in pancreatic bicarbonate output. Plasma concentrations of pancreatic polypeptide rose by 83 ± 16 pmol/l and were associated with a small reduction in trypsin, but no significant change in bilirubin outputs.     

Spontaneous Mitotic Recombination and Evidence for an X-Ray-Inducible System for the Repair of DNA Damage in DROSOPHILA MELANOGASTER

Spontaneous mitotic recombination in the left arm of chromosome 3 was examined in both unirradiated control flies and sibs irradiated early in development by determining the sizes and frequencies of multiple-wing-hair (mwh) clones in the wing blade of heterozygous mwh/+ flies. Approximately 16% of the spontaneous mwh clones arise from events generating cells with normal division rates. The remaining 84% result from events generating cells with an average cell division rate one-third that of the surrounding cells; these are thought to result from events that generate aneuploid cells. Such clones probably arise from a failure correctly to repair spontaneous DNA damage. The frequency of spontaneous events late in development decreases significantly after irradiation as much as 150 hours earlier in development. The suppression of spontaneous events decreases with a longer period of time between irradiation and the final cell divisions in the wing blade. These results suggest the existence of a repair system for DNA damage in Drosophila that is induced by irradiation. The decrease in effect with time following irradiation could result from slow degradation or dilution by subsequent cell growth and division.     

Outbreak analysis of an SIS epidemic model with rewiring

This paper is devoted to the analysis of the early dynamics of an SIS epidemic model defined on networks. The model, introduced by Gross et al. (Phys Rev Lett 96:208701, 2006), is based on the pair-approximation formalism and assumes that, at a given rewiring rate, susceptible nodes replace an infected neighbour by a new susceptible neighbour randomly selected among the pool of susceptible nodes in the population. The analysis uses a triple closure that improves the widely assumed in epidemic models defined on regular and homogeneous networks, and applies it to better understand the early epidemic spread on Poisson, exponential, and scale-free networks. Two extinction scenarios, one dominated by transmission and the other one by rewiring, are characterized by considering the limit system of the model equations close to the beginning of the epidemic. Moreover, an analytical condition for the occurrence of a bistability region is obtained.