Characterization of the sources of protein-ligand affinity: 1-sulfonato-8-(1'')anilinonaphthalene binding to intestinal fatty acid binding protein.

1-Sulfonato-8-(1')anilinonaphthalene (1,8-ANS) was employed as a fluorescent probe of the fatty acid binding site of recombinant rat intestinal fatty acid binding protein (1-FABP). The enhancement of fluorescence upon binding allowed direct determination of binding affinity by fluorescence titration experiments, and measurement of the effects on that affinity of temperature, pH, and ionic strength. Solvent isotope effects were also determined. These data were compared to results from isothermal titration calorimetry. We obtained values for the enthalpy and entropy of this interaction at a variety of temperatures, and hence determined the change in heat capacity of the system consequent upon binding. The ANS-1-FABP is enthalpically driven; above approximately 14 degrees C it is entropically opposed, but below this temperature the entropy makes a positive contribution to the binding. The changes we observe in both enthalpy and entropy of binding with temperature can be derived from the change in heat capacity upon binding by integration, which demonstrates the internal consistency of our results. Bound ANS is displaced by fatty acids and can itself displace fatty acids bound to I-FABP. The binding site for ANS appears to be inside the solvent-containing cavity observed in the x-ray crystal structure, the same cavity occupied by fatty acid. From the fluorescence spectrum and from an inversion of the Debye-Hueckel formula for the activity coefficients as a function of added salt, we inferred that this cavity is fairly polar in character, which is in keeping with inferences drawn from the x-ray structure. The binding affinity of ANS is considered to be a consequence of both electrostatic and conditional hydrophobic effects. We speculate that the observed change in heat capacity is produced mainly by the displacement of strongly hydrogen-bonded waters from the protein cavity.     

The Cellulases Endoglucanase I and Cellobiohydrolase II of Trichoderma reesei Act Synergistically To Solubilize Native Cotton Cellulose but Not To Decrease Its Molecular Size

Degradation of cotton cellulose by Trichoderma reesei endoglucanase I (EGI) and cellobiohydrolase II (CBHII) was investigated by analyzing the insoluble cellulose fragments remaining after enzymatic hydrolysis. Changes in the molecular-size distribution of cellulose after attack by EGI, alone and in combination with CBHII, were determined by size exclusion chromatography of the tricarbanilate derivatives. Cotton cellulose incubated with EGI exhibited a single major peak, which with time shifted to progressively lower degrees of polymerization (DP; number of glucosyl residues per cellulose chain). In the later stages of degradation (8 days), this peak was eventually centered over a DP of 200 to 300 and was accompanied by a second peak (DP, (apprx=)15); a final weight loss of 34% was observed. Although CBHII solubilized approximately 40% of bacterial microcrystalline cellulose, the cellobiohydrolase did not depolymerize or significantly hydrolyze native cotton cellulose. Furthermore, molecular-size distributions of cellulose incubated with EGI together with CBHII did not differ from those attacked solely by EGI. However, a synergistic effect was observed in the reducing-sugar production by the cellulase mixture. From these results we conclude that EGI of T. reesei degrades cotton cellulose by selectively cleaving through the microfibrils at the amorphous sites, whereas CBHII releases soluble sugars from the EGI-degraded cotton cellulose and from the more crystalline bacterial microcrystalline cellulose.     

Response of adult parasitoids ofBemisia tabaci (Hom.: Aleyrodidae) to leaf residues of selected cotton insecticides

The contact toxicity of eight insecticides to adults of four parasitoids of the sweetpotato whiteflyBemisia tabaci was evaluated in the laboratory. Two common Texas species,Eretmocerus sp. andEncarsia pergandiella Howard, and two exotic species,Eretmocerus mundus Mercet from Spain andEncarsia formosa Gahan from Greece were tested. Insecticides, applied as sprays to greenhouse-grown cotton plants at recommended rates were amitraz (Ovasyn^®), azinphosmethyl (Guthion^®), bifenthrin (Capture^®), buprofezin (Applaud^®), cypermethrin (Ammo^®), methyl parathion and thiodicarb (Larvin^®), with a water control. Parasitoid adults were confined on discs cut from leaves (1) sprayed the same day and (2) sprayed two days previously. Survival in both treatments was measured two and four days following exposure. Significant differences in toxicity were detected among the insecticides. Buprofezin was not toxic to any of the four parasitoids. When caged on leaves sprayed two days previously, only amitraz of the remaining compounds allowed significant general parasitoid survival after two days.E. mundus exhibited the greatest overall tolerance to insecticides, with 40% or more surviving 48 hr after confinement on leaves sprayed with amitraz, thiodicarb and cypermethrin. Survival was generally much reduced after 96 hr. In a separate test, fresh residues of endosulfan (Thiodan^®) were highly toxic at the two rates tested, but two day old residues at the lower rate allowed 76.7% survival ofE. mundus and 35% survival ofE. pergandiella after 48 hrs.     

Lipase-Catalyzed Regioselective Acylation and Deacylation of Glucose Derivatives

In the development of an efficient synthesis of 1-O-decanoyl-2,3,4,6-tetra-O-acetyl-β-D-glucose (β-2) several lipase-based approaches have been explored. Among five immobilized Upases tested, the lipase from Candida antarctica proved particularly efficient for catalyzing selective hydrolysis in the 1-position of 1,2,3,4,6-penta-O-acetyl-β-D-glucose (β-1). Using triethylamine as catalyst, the hydrolysis product 2,3,4,6-tetra-O-acetyl-D-glucose (3) can be esterified with decanoyl chloride to form β-2 selectively, thereby providing an efficient chemo-enzymatic synthesis starting from readily available raw materials. Attempts to produce β-2 from β-1 by lipase-catalyzed interesterification or to esterify 3 with decanoic acid using a lipase as catalyst were unsuccessful. The latter finding was explained by the hemiacetal OH group of glucose being unable to act as nucleophile in the lysis of the lipase acyl-enzyme intermediate. Furthermore, β-2 was found to bee a too bulky substrate to fit into the active site of any of the lipases tested.     

Simultaneous fructose and ethanol production from sucrose,usingZymomonas mobilis 2864 co-immobilised with invertase

Summary Fructokinase negativeZymomonas mobilis UQM 2864, was co-immobilised with invertase in alginate and incubated on sucrose-based media in batch and fedbatch culture. The highest fructose concentration achieved was 138 g/l using fed-batch cultivation with sugar-cane syrup-simultaneously producing 79.9 g/l or 10.1% (v/v) ethanol in less than 24 hours. The ethanol and fructose yields were 95 and 84% respectively. Co-immobilisation resulted in faster fermentation times, particularly for the batch fermentations, and complete utilisation of substrate.     

A PCR assay for the detection of Campylobacter jejuni and Campylobacter coli in water

A PCR assay has been developed for the detection of Campylobacter jejuni and Camp. coli in water samples. The sample is filtered through a membrane which is subjected to sonication to release the impacted cells. After removal of the filter from the cell suspension and a freeze/thaw cell lysis step, a semi-nested PCR is carried out on the filtrate using the primers CF02, CF03 and CF04 ( Camp. jejuni fla and flaB gene sequences). Incorporation of a sonication stage allows removal of the filter membrane since they have been shown to inhibit the PCR. In experiments with spiked water samples (20 ml) a theoretical sensitivity of 10–20 Campylobacter cells ml^-1 was achieved. Using a sample volume of 100 ml this sensitivity can be increased to approximately 2 Campylobacter cells ml^-1.