fimA-folD genes linkage in Salmonella identifies a putative junctional site of chromosomal rearrangement in the enterobacterial genome

Abstract Analysis of the Salmonella chromosomal region located upstream of the fimA gene (coding for the major type 1 fimbrial subunit) showed a close linkage of this gene to the folD gene (coding for the enzyme 5,10-methylenetetrahydrofolate dehydrogenase/5, 10-methenyltetrahydrofolate cyclohydrolase), indicating that the fim gene cluster of Salmonella , unlike that of Escherichia coli , has no regulatory genes located upstream of fimA and apparently terminates with this gene. The respective locations of the fim and folD genes in the E. coli and Salmonella genetic maps suggests that the fimA-folD intergenic region of Salmonella encompasses a junctional site of a genetic rearrangement that probably originated from the different chromosomal location of the fim genes in these species.     

Intracellular distribution of mammalian stress proteins. Effects of cytoskeletal-specific agents

Following a brief period of heat stress, the two highly conserved mammalian stress proteins, hsp68 and 70, were examined with respect to their intracellular locations. In four independent cell lines, hsp68 and 70 were found to partition into both Triton X-100-soluble and insoluble fractions as assessed by two-dimensional gel analysis of newly synthesized polypeptides, whereas a fifth cell line showed these proteins only in the Triton X-100-insoluble fraction. In addition, a previously described cell fractionation technique was utilized to gain information regarding the segregation of the two major mammalian stress proteins, hsp68 and 70, into distinct biochemically and morphologically characterized subcellular compartments of PtK2-epithelial cells. Two cytoskeletal-specific agents, taxol and colchicine, were also probed for their effects on the disposition of these polypeptides. Under our conditions of acute heat exposure, hsp68, 70 and their isoforms were globally distributed in all subcellular fractions examined, with a few notable exceptions in drug-treated cells. Colchicine, a microtubule-depolymerizing drug, inhibited the association of hsp68 and its variants with the double-detergent-extractable labile "cytoskeleton," whereas taxol, a microtubule-stabilizing agent, in some manner, facilitated the transit of hsp68 and its isovariants from a cytoplasmic to nuclear domain. Degree of cell density is a factor which influences the synthesis of various cytoskeletal proteins; therefore, we studied the effect of cell confluency on the disposition of mammalian stress proteins hsp68 and 70 in human FS-4 fibroblasts. In confluent cultures, where cell-cell contact was maximal, we observed the appearance of a previously undetected polypeptide which was not found in sparsely populated cultures. This protein may represent a post-translationally modified isoform of a preexisting heat shock protein, or perhaps, a novel stress protein.     

Psoralens sensitize glutathione photooxidation in vitro

In vitro experiments are reported showing that psoralens and other furocoumarins of current pharmacological interest, e.g., angelicin and 4,6,4'-trimethylangelicin, all have, to a variable extent, the ability to sensitize the photooxidation of glutathione in ethanol/phosphate buffer with pyrex-filtered ultraviolet light. Besides substrate concentration and the nature of the furocoumarin used, the rate of the sensitized reaction is markedly dependent on the partial pressure of oxygen and the pH of the medium, being progressively faster on passing from pH 5 to pH 8.5. Scavengers of superoxide ions (superoxide dismutase), hydrogen peroxide (catalase) and singlet oxygen (sodium azide, diazabicyclooctane, sorbic acid) have little or no inhibitory effect on the reaction rate. These and other data suggest that furocoumarins can directly sensitize glutathione photooxidation by forming a charge transfer complex which is driven to the oxidized products in the presence of oxygen. The possible relevance of these results to the mechanisms of skin melanin hyperpigmentation induced by furocoumarins and ultraviolet light is discussed.     

Hydrolysis and protection from hydrolysis of enkephalins in human plasma

Seven groups of enkephalin-degrading enzymes and three groups of inhibitors active on these enzymes were separated from human plasma. The activity of the enzymes in hydrolyzing enkephalins and of the inhibitors in protecting enkephalins from proteolysis was measured. Results obtained with the endogenous inhibitors were compared to those relative to synthetic inhibitors. Data obtained indicate that all enkephalin-degrading enzymes found in plasma are significantly inhibited by the endogenous substances present in this tissue. The inhibition of the different classes of plasma enzymes by two of the three groups of endogenous substances is quite uniform, while one group of inhibitors appears specific to dipeptidylpeptidases. Results obtained are discussed in terms of the functional role of the inhibitory substances and of the possible pharmacological implication of their presence in human plasma.     

Voltammetric studies on the electrochemical behaviour of membrane-entrapped hemes

Summary The electrochemical behaviour of Fe(III)-protoporphyrin IX entrapped into a cellulose triacetate membrane has been investigated by cyclic voltammetry. The physical entrapment into a solid matrix does not modify the redox properties of the entrapped berries, which also act as efficient promoters in the electrochemistry of cytochromec. Such a system represents a promising example of a simple solid-state promoter, and stimulates further investigations in order to obtain more complex systems that may be of significance for basic and applied bioelectrochemistry.     

The primary structure of donkey (Equus asinus) lysozyme contains the Ca(II) binding site of alpha-lactalbumin

The complete primary structure of donkey lysozyme has been established by pulsed liquid-phase sequencing of tryptic and chymotryptic peptides isolated by RP-HPLC. The positions of the Cys residues were identified by labeling the Cys residues with DABIA-reagent. Donkey lysozyme is a c-type lysozyme which is 129 amino acids long. It exhibits 50% homology to the human protein. We observe the full Ca(II) binding site suggested for the homologous alpha-lactalbumines. Although horse lysozyme has been reported to contain asparagine in position 61, which was in conflict with the three-dimensional structure of lysozyme, all other known c-type lysozymes, including donkey, contain Ser 61.     

Antibiotic resistance in strains of Listeria spp. from meat products

The susceptibility or resistance to 26 antimicrobial agents was determined for 64 strains of Listeria monocytogenes and 102 strains of L. innocua isolated from Italian meat products. Some strains of L. monocytogenes were found to be resistant to tetracycline, erythromycin, co-trimoxazole and clindamycin. No plasmids were found in any L. monocytogenes strain. Five strains of L. innocua contained a 7.9 kbp plasmid, but these isolates were not resistant to any antibiotic in common and treatment with curing agents could not eliminate resistance to antibiotics. These results suggest that antibiotic resistance was not likely to be plasmid mediated in our strains.     

Characterization of amine oxidases from pisum, lens, Lathyrus and Cicer

Amine oxidases have been purified to homogeneity from Pisum sativum, Lens esculenta, Lathyrus sativus and Cicer arietinum. The enzymes have a M_r. of 150 000 and are composed of two identical subunits of 72 000. The amine oxidases showed an isoelectrophoretic heterogeneity.     

beta-Internexin, a ubiquitous intermediate filament-associated protein

In this article we show a Triton-insoluble, intermediate filament-associated protein of approximately 70 kD to be expressed ubiquitously in diverse mammalian cell types. This protein, assigned the name beta-internexin, exhibits extreme homology in each of the various cell lines as demonstrated by identical limited peptide maps, similar mobilities on two-dimensional gels, and detection in Triton-soluble and -insoluble extracts. beta-Internexin also shares some degree of homology with alpha-internexin, an intermediate filament-associated protein isolated and purified from rat spinal cord, which accounts for the immunologic cross-reactivity displayed by these polypeptides. Light microscopic immunolocalization of beta-internexin with a monoclonal antibody (mAb-IN30) reveals it to be closely associated with the vimentin network in fibroblasts. The antigen is also observed to collapse with the vimentin reticulum during the formation of a juxtanuclear cap induced by colchicine treatment. Ultrastructural localization, using colloidal gold, substantiates the affinity of beta-internexin for cytoplasmic filaments and, in addition, demonstrates its apparent exclusion from the intranuclear filament network. We examine also the resemblance of beta-internexin to a microtubule-associated polypeptide and the constitutively synthesized mammalian heat shock protein (HSP 68/70).     

Monolayer black membranes from bipolar lipids of archaebacteria and their temperature-induced structural changes

The membrane of Caldariella acidophila, an extreme thermophilic archaebacterium, is characterized by unusual bipolar complex lipids. They consist of two nonequivalent polar heads, linked by a C40 alkylic component. The molecular organization of these lipids in the plasma membrane is still a matter of study. In this paper, we present current-voltage measurements on artificial bipolar lipid membranes, indicating that molecules are indeed organized as a covalently bound bilayer, in which each molecule is completely stretched and spans its entire thickness. Furthermore, conformational transitions of these artificial membranes (which could be formed only above 70 degrees C from a lipid/squalene dispersion) are analyzed in the 80 to 15 degrees C temperature range. Abrupt variations in capacitance and valinomycin-induced conductance seem to indicate the occurrence of at least two structural changes. Measurements are also extended to different solvent systems. Results are consistent with the picture of a monolayer bipolar lipid membrane in which few solvent molecules align themselves parallel to the lipophilic chains. The amount of solvent as well as the temperature at which conformational transitions occur, depend on the solvent system in which the lipid is dispersed.