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A method for detecting structure in marginally stable forms of a protein is described. The principle is to measure amide proton exchange rates in the absence and presence of varying concentrations of a denaturant. Unfolding of structure by the denaturant is reflected by an acceleration of amide proton exchange rates, after correction for the effects of the denaturant on the intrinsic rate of exchange. This exchange-rate test for structure makes no assumptions about the rate of exchange in the unfolded state. The effects of 0-8 M urea and 0-6 M guanidinium chloride (GdmCl) on acid- and base-catalyzed exchange from model compounds have been calibrated. GdmCl does not appear to be well-suited for use in the exchange-rate test; model compound studies show that the effects of GdmCl on intrinsic exchange rates are complicated. In contrast, the effects of urea are a more uniform function of denaturant concentration. Urea increases acid-catalyzed, and decreases base-catalyzed, rates in model compounds. The exchange-rate test is used here to study structure formation in the S-protein (residues 21-124 of ribonuclease A). In conditions where an equilibrium folding intermediate of S-protein (I3) is known to be populated (pH 1.7, 0 degree C), the exchange-rate test for structure is positive. At higher temperatures (greater than 32 degrees C) I3 is unfolded, but circular dichroism data suggest that residual structure remains [Labhardt, A. M. (1982) J. Mol. Biol. 157, 357-371].(ABSTRACT TRUNCATED AT 250 WORDS)

Ocimum gratissimum leaf extracts have been extensively demonstrated to be effective against the various aetiologic agents of diarrhoea, including Shigellae. However, the mechanism of the shigellocidal action of this plant remains to be understood. This study investigated the effects of O. gratissimum essential oil (EO) at subinhibitory concentrations of 0.75 and 1.0 microg/ml on virulence and multidrug-resistant strains of 22 Shigella isolates from Nigeria. Compared with untreated Shigella strains, O. gratissimum EO caused significant decreases (p<0.01) in extracellular protease activity, o-lipopolysaccharide rhamnose content and incidence of invasiveness mediated as keratoconjunctivitis in guinea pig. The disparity in extracellular protease activity and o-lipopolysacharide rhamnose between the two treatment groups was also found to be significant (p<0.05), suggesting greater anti-virulent effects of O. gratissimum oil at 1.0 microg/ml. Antibiotic susceptibility testing revealed that the EO of O. gratissimum reduced the MICs of antibiotics to which Shigellae showed resistance by 9.8-53.1% and fluoroquinolones by 18.2-45.5%. The results of this study strongly suggest inhibition of extracellular protease and expression of O-LPS rhamnose in Shigellae by O. gratissimum EO. The future use of O. gratissimum- antibiotic combinations as a therapeutic measure against shigellosis is discussed.

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A dye-decolorizing bacterium was isolated from a soil sample and identified as Bacillus thuringiensis using 16S rRNA sequencing. The bacterium was able to decolorize three different textile dyes, namely, Reactive blue 13, Reactive red 58, and Reactive yellow 42, and a real dyehouse effluent up to 80-95% within 6 h. Some non-textile industrially important dyes were also decolorized to different extents. Fourier transform infrared spectroscopy and gas chromatography-mass spectrometer analysis of the ethyl acetate extract of Congo red dye and its metabolites showed that the bacterium could degrade it by the asymmetric cleavage of the azo bonds to yield sodium (4- amino-3-diazenylnaphthalene-1-sulfonate) and phenylbenzene. Sodium (4-amino-3-diazenylnaphthalene-1-sulfonate) was further oxidized by the ortho-cleavage pathway to yield 2- (1-amino-2-diazenyl-2-formylvinyl) benzoic acid. There was induction of the activities of laccase and azoreductase during the decolorization of Congo red, which suggests their probable role in the biodegradation. B. thuringiensis was found to be versatile and could be used for industrial effluent biodegradation.

A surface membrane 3'-nucleotidase from Leishmania donovani promastigotes has been purified to SDS/PAGE homogeneity. The enzyme has apparent subunit molecular mass of 38 kDa, pI 5.8 and a broad pH optimum, 5.5-7.5. EDTA partially inhibited the enzyme activity, which was fully restored by Co2+; Mg2+, Ca2+ or Mn2+ had no effect on the activity. ZnCl2 or dithiothreitol at 1 mM was inhibitory at pH 7.5, but was without effect at pH 5.5, whereas at both pH values 5 mM of either compound inhibited the enzyme. The substrate-specificity of the purified enzyme is restricted to ribonucleoside 3'-phosphates. 3'-AMP and 3'-IMP are the best substrates, whereas ADP, ATP, 2'-deoxyadenosine 3'-phosphate and 5'-AMP are competitive inhibitors of the enzyme. The enzyme showed low latency in intact-cell preparations. The kinetic properties and the surface membrane localization of the enzyme suggest its implication in the formation of nucleosides from 3'-nucleotides of the parasite's host.

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In a study to isolate fungal pathogens with potential for the biocontrol of water hyacinth (Eichhornia crassipes), some lakes in the Lagos State and its environs, Nigeria, were surveyed for diseased water hyacinth (E. crassipes). The fungi present in the diseased tissue were isolated and identified as: Aspergillus niger, Aspergillus flavus, Penicillium sp., Curvularia pallescens, Fusarium solani and Myrothecium roridum. The pathogenicity of isolates of these fungi on fresh, non-diseased water hyacinth plants was investigated. Myrothecium was the only species capable of inducing disease symptoms. Necrosis was observed on water hyacinth leaves three days post inoculation (DPI) with M. roridum (1 × 10 6 spores/ml). The leaves and the petioles were withered at the end of day 24, and the disease incidence and disease severity were 100% and 8.67%, respectively. Molecular analysis of the internal transcribed spacer rDNA of the M. roridum isolate from water hyacinth showed >98% homology to authenticated sequences of M. roridum. The isolate, deposited at the International Mycological Institute, UK, as M. roridum Tode: Fries (IMI 394934), possesses the level of virulence needed in a potential mycoherbicide for use in the management of water hyacinth.