Structure of the Escherichia coli heptosyltransferase WaaC: binary complexes with ADP and ADP-2-deoxy-2-fluoro heptose

Lipopolysaccharides constitute the outer leaflet of the outer membrane of Gram-negative bacteria and are therefore essential for cell growth and viability. The heptosyltransferase WaaC is a glycosyltransferase (GT) involved in the synthesis of the inner core region of LPS. It catalyzes the addition of the first L-glycero-D-manno-heptose (heptose) molecule to one 3-deoxy-D-manno-oct-2-ulosonic acid (Kdo) residue of the Kdo2-lipid A molecule. Heptose is an essential component of the LPS core domain; its absence results in a truncated lipopolysaccharide associated with the deep-rough phenotype causing a greater susceptibility to antibiotic and an attenuated virulence for pathogenic Gram-negative bacteria. Thus, WaaC represents a promising target in antibacterial drug design. Here, we report the structure of WaaC from the Escherichia coli pathogenic strain RS218 alone at 1.9 A resolution, and in complex with either ADP or the non-cleavable analog ADP-2-deoxy-2-fluoro-heptose of the sugar donor at 2.4 A resolution. WaaC adopts the GT-B fold in two domains, characteristic of one glycosyltransferase structural superfamily. The comparison of the three different structures shows that WaaC does not undergo a domain rotation, characteristic of the GT-B family, upon substrate binding, but allows the substrate analog and the reaction product to adopt remarkably distinct conformations inside the active site. In addition, both binary complexes offer a close view of the donor subsite and, together with results from site-directed mutagenesis studies, provide evidence for a model of the catalytic mechanism.     

Comparative functional characterization in vitro of heptosyltransferase I (WaaC) and II (WaaF) from Escherichia coli.

Heptosyltransferase II, encoded by the waaF gene of Escherichia coli, is a glycosyltransferase involved in the synthesis of the inner core region of lipopolysaccharide. The gene was subcloned from plasmid pWSB33 [Brabetz, W., Müller-Loennies, S., Holst, O. & Brade, H. (1997) Eur. J. Biochem. 247, 716-724] into a shuttle vector for the expression in the gram-positive host Corynebacterium glutamicum. The in vitro activity of the enzyme was investigated in comparison to that of heptosyltransferase I (WaaC) using as a source for the sugar nucleotide donor, ADP-LglyceroDmanno-heptose, a low molecular mass filtrate from a DeltawaaCF E. coli strain. Synthetic lipid A analogues varying in the acylation or phosphorylation pattern or both were tested as acceptors for the subsequent transfer of 3-deoxy-Dmanno-oct-2-ulosonic acid (Kdo) and heptose by successive action of Kdo transferase (WaaA), heptosyltransferase I (WaaC) and heptosyltransferase II (WaaF). The reaction products were characterized after separation by TLC and blotting with monoclonal antibodies specific for the acceptor, the intermediates and the final products.     

OpsX from Haemophilus influenzae represents a novel type of heptosyltransferase I in lipopolysaccharide biosynthesis

The inner core region of the lipopolysaccharide (LPS) of Haemophilus influenzae is characterized by the presence of a phosphorylated 3-deoxy-alpha-D-manno-octulosonic acid (Kdo). In this study, we show that the heptosyltransferase I adding the first L-glycero-D-manno-heptose residue to this acceptor is encoded by the gene opsX, which differs in substrate specificity from the other heptosyltransferase I, known as WaaC.     

Effect of lacZY-marking of the 2,4-diacetyl-phloroglucinol producing Pseudomonas fluorescens-strain 5-2/4 on its physiological performance and root colonization ability

Transgenic Pseudomonas fluorescens 5-2/4 with reinforced 2,4-diacetyl phloroglucinol (phl) production had shown increased biocontrol ability towards Pythium ultimum (Pu), but inferior root colonization ability compared to its wild type 5.014. Therefore, enhanced root colonization ability of the transgenic strain by repeated inoculation and reisolation on tomato plants was suggested. As a preparation for repeated inoculation and reisolation cycles, the construction of a negative control of the transgenic strain 5-2/4 by marking with lacZY and screening for a mutant possessing qualities comparable to 5-2/4 was performed. Morphologically, colonies of all of the 11 selected mutants were similar on MLXgal medium. The root colonization ability of two of the lacZY-marked strains (mutants 1 and 10) was comparable to the parental strain. These were also able to compete with the resident microflora of tomato seedlings to the same extent as the parental strain. Five mutants were excluded due to lower growth rates on Yeast Malt, King's B Medium (KB) and 0.1 Tryptic Soy Agar (mutant 4, 5 and 8), excessive growth and higher siderophore production on KB (mutant 10) and increased protease production (mutant 2). With respect to in vitro-antagonism of Pu, no differences could be found between the target strain and mutants 1, 3, 6, 7 and 9. Examination of sole carbon source utilization of these five lacZY-marked strains revealed a significantly higher utilization of alpha-D-lactose and lactulose compared to 5-2/4. However, significant differences could be found for 51% of the utilized carbon sources. Cluster analysis showed a high degree of similarity between 5-2/4 and mutant 1 both when analyzed with and without alpha-D-lactose. As mutant 1 also represented the colonization pattern most similar to the parental strain 5-2/4, it presents a presumptive subject for a negative control in the following inoculation and reisolation studies on tomato.     

Effect of light on the nucleotide composition of rRNA of wheat seedlings

Both qualitative and quantitative differences in the minor nucleotide constituents of rRNA from normally grown and from etiolated wheat plants (Triticum aestivum L.) were established. Using different degradation methods and separation techniques the 18S+26S RNA of 8-day-old wheat seedlings grown in the light was found to contain 5-methylcytidine, 3-methylcytidine, 5-methyluridine, 3-methyluridine, 5-carboxymethyluridine, 1-methyladenine, N-methyladenine, 5-hydroxymethylcytidine, O²-methyluridine, O²-methylcytidine, pseudouridine, O²-methylpseudouridine, N²,N²-dimethylguanine, 1-methylguanine, ribothymidine and some unknown minor constituents. On the other hand, there were only a few minor nucleotides in the rRNA of etiolated wheat seedlings. Cycloheximide, a cytoplasmic protein synthesis inhibitor, simulated etiolation in that it reduced the number of minor nucleotides in rRNA, whereas chloramphenicol, a chloroplast protein synthesis inhibitor, had no significant effect on the minor nucleotide content of rRNA. This finding suggests that illumination may cause de novo synthesis of cytoplasmic modifying enzymes leading to the formation of highly modified rRNAs.Abbreviations m⁶A N⁶-methyladenine - m¹A 1-methyladenine - 5hmc 5-hydroxymethylcytidine - Cm O²-methylcytidine - m⁵C 5-methylcytidine - m³C 3-methylcytidine - m¹G 1-methylguanine - m ₂ ² G N², N²-dimethylguanine - pseudouridine - m O²-methylpseudouridine - Um O²-methyluridine - m³U 3-methyluridine - m⁵U 5-methyluridine - cm⁵U 5-carboxymethyluridine - rT ribothymidine - Pur purine - Pyr pyrimidine - RNase ribonuclease - UV ultra violet - p phosphate     

Rapid detection of the alternativeN-glycosylation pathway using high pH anion exchange chromatography

An alternativeN-glycosylation pathway using Glc_1–3Man₅GlcNAc₂ as a donor to be transferred to a protein acceptor is found either in Man-P-Dol synthase deficient cells or in wild type CHO cells grown in energy deprivation conditions. Discrimination between oligomannosides of this alternative pathway and oligomannosides of the major one containing the same number of sugar residues Man_6–8GlcNAc₂ required structural studies. Taking advantage of the specific chromatographic behaviour of glucosylated oligomannosides, in pellicular high pH anion exchange chromatography, we developed a one-step method for the identification of the alternativeN-glycosylation pathway compounds differing from those of the major one.Abbreviations HPAEC high pH anion exchange chromatography - endo H endo betaN-acetylglucosaminidase H - PNGaseF peptideN-glycosidase F - M2 Man₂GlcNAc₂ - M4 Man₄GlcNAc₂ - M5 Man₅GlcNAc₂ - G1M5 Glc₁Man₅GlcNAc₂ - G2M5 Glc₂Man₅GlcNAc₂ - G3M5 Glc₃Man₅GlcNAc₂ - M6 Man₆GlcNAc₂ - M8 Man₈GlcNAc₂ - M9 Man₉GlcNAc₂ - G1M9 Glc₁Man₉GlcNAc₂ - G2M9 Glc₂Man₉GlcNAc₂ - G3M9 Glc₃Man₉GlcNAc₂ To whom correspondence should be addressed.     

Isolation and properties of a sialidase fromTrypanosoma rangeli

In the culture supernatant ofTrypanosoma rangeli, strain El Salvador, a sialidase was present with an activity of 0.1 U/mg protein as determined with the 4-methylumbelliferyl glycoside of -N-acetylneuraminic acid as substrate. This enzyme was purified about 700-fold almost to homogeneity by gel chromatography on Sephadex G-100 and Blue Sepharose, and affinity chromatographies on 2-deoxy-2,3-didehydroneuraminic acid and horse submandibular gland mucin, both immobilized on Sepharose. The pH optimum is at 5.4–5.6, and the molecular weight was determined by gel chromatography, high performance liquid chromatography and sodium dodecyl sulphate gel electrophoresis to be 70 000. The substrate specificity of the enzyme is comparable to bacterial, viral and mammalian sialidases with cleavage rates for the following substrates in decreasing order: N-acetylneuraminyl-(2–3)-lactose> N-glycoloylneuraminy-(2–3)-lactose> N-acetylneuraminyl-(2–6)-lactose >sialoglycoproteins>gangliosides>9-O-acetylated sialoglycoproteins.4-O-Acetylated derivatives are resistant towards the action of this sialidase. The enzyme activity can be inhibited by 2-deoxy-2,3-didehydro-N-acetylneuraminic acid, Hg²⁺ ions, andp-nitrophenyloxamic acid; it is not dependent on the presence of Ca²⁺ Mn²⁺ or Mg²⁺ ions.Abbreviations BSA bovine serum albumin - BSM bovine submandibular gland mucin - CMP cytidine monophosphate - EDIA ethylenediaminetetraacetic acid - ESM equine submandibular gland mucin - HEPES N-2-hydroxyethylpiperazine-N-2-ethanesulfonic acid - HPLC high performance liquid chromatography - Lac lactose - MU-Neu5Ac 4-methylumbelliferyl glycoside of -N-acetylneuraminic acid - Neu5Ac N-acetylneuraminic acid - Neu5Ac2en 2-deoxy-2,3-didehydro-N-acetylneuraminic acid - Neu4Ac5Gc N-glycoloyl-4-O-acetylneuraminic acid - Neu2en 2-deoxy-2,3-didehydroneuraminic acid - Neu5Gc N-glycoloylneuraminic acid - PMSF phenylmethylsulfonyl fluoride - PSM pig submandibular gland mucin - SDS sodium dodecyl sulfate - Tris tris-(hydroxymethyl)aminomethane Dedicated to Professor Dr. Heinz Mühlpfordt on the occasion of his 65th birthday.     

Synthesis of Neu5Ac- and Neu5Gc-α-(2→6′)-lactosamine 3-aminopropyl glycosides

In order to prepare 3-aminopropyl glycosides of Neu5Ac-α-(2→6′)-lactosamine trisaccharide 1, and its N-glycolyl containing analogue Neu5Gc-α-(2→6′)-lactosamine 2, a series of lactosamine acceptors with two, three, and four free OH groups in the galactose residue was studied in glycosylations with a conventional sialyl donor phenyl [methyl 5-acetamido-4,7,8,9-tetra-O-acetyl-3,5-dideoxy-2-thio- -glycero-α- and β- -galacto-2-nonulopyranosid]onates (3) and a new donor phenyl [methyl 4,7,8,9-tetra-O-acetyl-5-(N-tert-butoxycarbonylacetamido)-3,5-dideoxy-2-thio- -glycero-α- and β- -galacto-2-nonulopyranosid]onates (4), respectively. The lactosamine 4′,6′-diol acceptor was found to be the most efficient in glycosylation with both 3 and 4, while imide-type donor 4 gave slightly higher yields with all acceptors, and isolation of the reaction products was more convenient. In the trisaccharides, obtained by glycosylation with donor 4, the 5-(N-tert-butoxycarbonylacetamido) moiety in the neuraminic acid could be efficiently transformed into the desired N-glycolyl fragment, indicating that such protected oligosaccharide derivatives are valuable precursors of sialo-oligosaccharides containing N-modified analogues of Neu5Ac.     

Bacteriochlorophyll c monomers,dimers, and higher aggregates in dichloromethane,chloroform, and carbon tetrachloride

Bacteriochlorophyll c in vivo is a mixture of at least 5 homologs, all of which form aggregates in CH₂Cl₂, CHCl₃ and CCl₄. Three homologs exist mainly in the 2-R-(1-hydroxyethyl) configuration, whereas the other two homologs, 4-isobutyl-5-ethyl and 4-isobutyl-5-methyl farnesyl bacteriochlorophyll c, exist mainly in the 2-S-(1-hydroxyethyl) configuration (Smith KM, Craig GW, Kehres LA and Pfennig N (1983) J. Chromatograph. 281: 209–223). In CCl₄ the S-homologs form an aggregate of 2–3 molecules whose absorption (747 nm maximum) and circular dichroism spectra resemble those of the chlorosome. In CH₂Cl₂, CHCl₃ and CCl₄ the 4-n-propyl homolog (R-configuration) forms dimers absorbing at ca. 680 nm and higher aggregates absorbing at 705–710 nm. In CCl₄ the dimerization constant is approx. 10 µM^–1 (1000 times that for chlorophyll a). The difference between the types of aggregates formed by the 4-n-propyl and 4-isobutyl homologs is attributed to the difference between the R- and S-configurations of the 2-(1-hydroxyethyl) groups in each chlorophyll.Abbreviations BChl bacteriochlorophyll - CD circular dichroism - Chl chlorophyll - DNS data not shown - EEF 4-ethyl-5-ethyl farnesyl - iBM/EF 4-isobutyl-5-methyl/ethyl farnesyl - MEF 4-methyl-5-ethyl farnesyl - PEP 4-n-propyl-5-ethyl farnesyl     

Structural determination of the oligosaccharides in the milk of an Asian elephant (Elephas maximus)

Milk of an Asian elephant (Elephas maximus), collected at 11 days post partum, contained 91 g/L of hexose and 3 g/L of sialic acid. The dominant saccharide in this milk sample was lactose, but it also contained isoglobotriose (Glc(alpha1-3)Gal(beta1-4)Glc) as well as a variety of sialyl oligosaccharides. The sialyl oligosaccharides were separated from neutral saccharides by anion exchange chromatography on DEAE-Sephadex A-50 and successive gel chromatography on Bio Gel P-2. They were purified by high performance liquid chromatography (HPLC) using an Amide-80 column and characterized by 1H-NMR spectroscopy. Their structures were determined to be those of 3'-sialyllactose, 6'-sialyllactose, monofucosyl monosialyl lactose (Neu5Ac(alpha2-3)Gal(beta1-4)[Fuc(alpha1-3)]Glc), sialyl lacto-N-neotetraose c (LST c), galactosyl monosialyl lacto-N-neohexaose, galactosyl monofucosyl monosialyl lacto-N-neohexaose and three novel oligosaccharides as follows: Neu5Ac(alpha2-3)Gal(beta1-4)[Fuc(alpha1-3)]GlcNAc(beta1-3)Gal(beta1-4)Glc, Neu5Ac(alpha2-6)Gal(beta1-4)GlcNAc(beta1-3)Gal(beta1-4)GlcNAc(beta1-3)Gal(beta1-4)Glc, and Neu5Ac(alpha2-3)Gal(beta1-4)[Fuc(alpha1-3)]GlcNAc(beta1-3)Gal(beta1-4)[Fuc(alpha1-3)]GlcNAc(beta1-3)Gal(beta1-4)Glc. The higher oligosaccharides contained only the type II chain (Gal(beta1-4)GlcNAc); this finding differed from previously published data on Asian elephant milk oligosaccharides.     

Anti-fungal effects of phenolic amides isolated from the root bark of Lycium chinense

Four phenolic amides, dihydro-N-caffeoyltyramine (1), trans-N-feruloyloctopamine (2), trans-N -caffeoyltyramine (3), and cis-N-caffeoyltyramine (4), were isolated from an ethyl acetate extract of the root bark of Lycium chinense Miller. All had an anti-fungal effect; compounds 1-3 were potent at 5-10 microg ml(-1) and were without hemolytic activity against human erythrocyte cells. Compound 4 was active at 40 microg ml(-1). All four compounds impeded the dimorphic transition of pathogen, Candida albicans.     

Asialo-α1-acid glycoprotein resialylated with 9-amino-5-N-acetyl-d-neuraminic acid is resistant towards bacterial,viral and mammalian sialidases

We demonstrate that 9-amino-NeuAc transferred to asialo-₁-acid glycoprotein resists cleavage by bacterial, viral and mammalian sialidases. This is the first synthetic sialic acid analogue, which can be activated and transferred to glycoprotein, but is not a sialidase (EC 3.2.1.18) substrate.Abbreviations HPLC high performance liquid chromatography - BSA bovine serum albumin - NeuAc N-acetyl-d-neuraminic acid, 5-acetamido-3,5-dideoxy-d-glycero-d-galacto-non-2-ulosonic acid - 9-Amino-NeuAc 9-amino-5-N-acetyl-d-neuraminic acid, 5-acetamido-9-trideoxy-d-glycero-d-galacto-non-2-ulosonic acid - CMP-NeuAc cytidine-5-monophospho-N-acetyl-d-neuraminic acid - CMP-9-amino-NeuAc cytidine-5-monophospho-9-amino-5-N-acetyl-d-neuraminic acid - 9-azido-NeuAc 5-acetamido-9-azido-3,5,9-trideoxy-d-glycero-d-galacto-non-2-ulosonic acid. Enzymes EC 3.2.1.18 sialidase, acylneuraminylhydrolase - EC 2.4.99.1 Galß1-4GlcNAc a(2-6)-sialytransferase     

Factors affecting the glucosylation capacity of cell cultures of Datura innoxia and Scopolia carniolica for monophenolic compounds

Suspension grown cells of Datura innoxia and Scopolia carniolica were tested for their glucosylation capacity and some factors affecting the efficiency of the reaction were studied.Cells at the end of the exponential growth phase showed a high glucosylation capacity. Light conditions had little effect on the bioconversion reaction. For the substrates hydroquinone and p-hydroxybenzoic acid the bioconversions were concentration-dependent. Permeabilization with propanol diminished the bioconversion capacity. Depending on the substrate used, relatively large amounts of substrate and product could not be recovered. Tannic acid could partly prevent decomposition of the compounds. The bioconversion capacity of cultures with a low glucosylation capacity could be enhanced by addition of uridine diphosphate-glucose, indicating that the sugar donor is a critical factor. From six substrates the natural compounds hydroquinone, p-hydroxybenzoic acid and vanillin were glucosylated. No glucosides were detected from tyramin and two synthetic aminotetralines.Abbreviations 5HAT 5-hydroxyaminotetralin - NO437 2-(N-propyl-N-2-thienylamino)-5-hydroxytetraline - pHBA p-hydroxybenzoic acid - UDP-glucose uridine diphosphate-glucose     

Lignin degradation byPhanerochaete chrysosporium: Metabolism of a phenolic phenylcoumaran substructure model compound

The degradation of a lignin substructure model compound, 5-formyl-3-hydroxymethyl-2-(4-hydroxy-3,5-dimethoxyphenyl)-7-methoxycoumaran (I), in ligninolytic culture of a white-rot wood decay fungus,Phanerochaete chrysosporium, was investigated. It was found that I was hydroxylated or dehydrogenated in its coumaran ring to give 2-(5-formyl-2-hydroxy-3-methoxyphenyl)-3-hydroxypropiosyringone (II) and two coumarones, 5-formyl-3-hydroxymethyl-2-(4-hydroxy-3,5-dimethyoxyphenyl)-7-methoxycoumarone (V) and 3,5-diformyl-2-(4-hydroxy-3,5-dimethoxyphenyl)-7-methoxycoumarone (VI), II was further converted to 2,6-dimethoxy-p-benzoquinone (IV), syringic acid (III), and 5-carboxyvanillic acid (VIII). These metabolic products were identified by mass spectrometric comparison with the authentic compounds. A proposed pathway for the degradation of I is presented on the basis of these metabolic products. The degradation could be catalyzed mainly by phenol-oxidizing enzymes.Non-Standard Abbreviations TLC thin layer chromatography     

Expression of recombinant rabbit UDP-GlcNAc:α3-d-mannoside β-1,2-N-acetylglucosaminyltransferase I catalytic domain in Sf9 insect cells

UDP-GlcNAc:3-d-mannoside -1,2-N-acetylglucosaminyltransferase I (GnT I; EC 2.4.1.101) catalyses a key reaction in the conversion of oligomannose to complex and hybridN-glycans. The cytoplasmic tail and transmembrane segment of rabbit GnT I cDNA were replaced with an in-frame cleavable signal sequence and the hybrid construct was inserted into the genome ofAutographa californica nuclear polyhedrosis virus (AcMNPV) under the control of the polyhedrin promoter. Sf9 insect cells were infected with the recombinant baculovirus and the enzymatically active and soluble catalytic domain of GnT I was purified from the medium (1–5 mg 1^–1) in two steps to a specific activity of abut 2 µmol min^–1 mg^–1 protein. Recombinant GnT I has been used for the chemical-enzymatic synthesis of analogues of Man1-6[GlcNAc1-2Man1-3]Man-O-octyl.Abbreviations AcMNPV Autographa californica nuclear polyhedrosis virus - FCS fetal calf serum - 1 µmol min^–1 international enzyme unit - MAG myelin associated glycoprotein - MOI multiplicity of infection - pfu plaque forming units - SDS-PAGE sodium dodecyl sulfate/polyacrylamide gel electrophoresis - Sf9 cells Spodoptera frugiperda insect cells - GnT I UDP-GlcNAc:3-d-mannoside 1,2-N-acetylglucosaminyltransferase I (EC 2.4.1.101)     

Reversing the inhibitory effect of paclobutrazol on seed germination of Amaranthus paniculatus by GA3, ethephon or ACC

The germination of Amaranthus paniculatus seeds was inhibited by applying paclobutrazol, a specific inhibitor of gibberellin biosynthesis. This inhibition was markedly counteracted by gibberellin A₃ (GA₃), suggesting that endogenous gibberellins are required for germination in this species. The inhibitory effect of paclobutrazol was also overcome by ethephon (2-chloroethylphosphonic acid) or the precursor of ethylene biosynthesis, ACC (1-aminocyclopropane-l-carboxylic acid). Thus the physiological effect of gibberellin can be mimicked by ethylene released from ethephon or synthesised from exogenous ACC. It is suggested, that endogenous gibberellins are involved in germination of Amaranthus paniculatus seeds and that action of GA₃ can be substituted by ethylene.Abbreviations ACC 1-aminocyclopropane-l-carboxylic acid - AMO-1618 (2-isopropyl-5methyl-4-trimethylammoniumchloride)-phenyl-l-piperidinium-carboxylate - ancymidol -cyclopropyl--(4-methoxyphenyl)-5-pyrimidine methanol - chloromequat chloride (2-chloroethyl)trimethylammoniumchloride - ethephon 2-chloroethylphosphonic acid - GA gibberellin A₃ - paclobutrazol (2RS, 3RS)-1-(4-chlorophenyl)-4,4-dimethyl-2-(1,2,4-triazol-lyl)pentan-3-ol - Phosphon D 2,4,dichlorobenzyl-tributhylphosphoniumchloride - tetcyclacis 5,(4-chlorophenyl)-3,4,5,9,10-pentaaza-tetracyclo)5,4,1,0,Z,6,0^8,11 dodeca-3,9-diene     

Immediate effects of pyridazinone herbicides on photosynthetic electron transport in algal systems

Pyridazinone herbicides, SANDOZ 9785 (4-chloro-5-dimethylamino2-phenyl-3-(2H) pyridazinone), SANDOZ 9789 (4-chloro-5 (methylamino)-2-(α, α, α-trifluoro-m-tolyl-3-(2H) pyridazinone) and SANDOZ 6706 (4-chloro-5-(methylamino)-2-(α, α, α-trifluoro-m-tolyl-3-(2H) pyridazinone) inhibited photosystem II electron transport inChlorella protothecoides, when the herbicides were added to the assay medium. The inhibitory eficiency varied with the algal species and the nature of substitution of pyridazinones. Using 3 algal systemsviz., Chlorella, Scenedesmus andAnacystis, the I₅₀ value of for the inhibition of photosynthesis of 3 substituted pyridazinones (SANDOZ 9785, SANDOZ 6706 and SANDOZ 9789) were determined. SANDOZ 9789 was found to be the weakest inhibitor of photosystem II electron transport (H₂O→ benzoquinone) as compared to SANDOZ 9785 and SANDOZ 6706. In general, the order of inhibition could be given as SANDOZ 6706 >- SANDOZ 9785 > SANDOZ 9789. The I₅₀ value of photosynthetic particles obtained fromChlorella cells was similar to that of whole cells, suggesting that the cell wall ofChlorella did not act as a barrier for the herbicide action. Studies on the light intensity dependence of SANDOZ 9785 inhibition of electron transport (H₂O→ benzoquinone) showed that the light-dependent portion of the curve was more sensitive than the light independent portion of the curve. It is suggested that the site of action was on the reducing side of photosystem II.     

Diastereoselective hydroxylation and reduction of derivatised tetrahydrofurans by Beauveria bassiana

The filamentous fungus, Beauveria bassiana ATCC 7159, catalyses the regio- and diastereoselective biohydroxylation of trans-2-methyl-5-benzyloxymethyl-tetrahydrofuran to the cis-3-hydroxy derivative. When incubated with cis-2-methyl-3-keto-5-benzyloxymethyltetrahydrofuran, the same fungus performs a reduction to give the cis- and trans-alcohols in a 4:1 ratio.     

Antischistosomal action of thioxo-imidazolidine compounds: an ultrastructural and cytotoxicity study

Schistosomiasis is a disease caused by helminthes of the genus Schistosoma, which threatens approximately 207 million people worldwide. Recently, strains of Schistosoma mansoni appear to be developing tolerance and resistance against Praziquantel, the most commonly available drug on the market used in the treatment of disease. This worrisome development justifies studies that seek alternatives for the prevention, treatment and cure of this disease. This study aimed to evaluate the in vitro activity of new imidazolidine compounds 1-benzyl-4-[(4-chloro-phenyl)-hydrazono]-5-thioxo-imidazolidin-2-one (LPSF/PT-5) and 1-(4-chloro-benzyl)-4-[(4-fluoro-phenyl)-hydrazono]-5-thioxo-imidazolidin-2-one (LPSF/PT-11) against adult worms of S. mansoni. LPSF/PT-5 and LPSF/PT-11 imidazolidine derivatives showed relevant schistosomicidal activity in vitro and induced significant ultrastructural alterations in worms and cell death: results similar to praziquantel. Thus, it is possible that these imidazolidine derivatives can be future candidates as schistosomotic drugs, but further studies are needed to elucidate the induced mechanisms behind this response.