Microcomputer BASIC programs for rapid determination of lethal dosages of biocides using logit transformations

The probit analysis model is generally used for the deterininationof lethal dosages in bioassay applications. However, the logitmodels, which use the logistic curve instead of the integratednonnal curve, could also be effectively used for the determinationof lethal dosages and regression coefficients. In this paper,two lypes of logit models, namely minimum logit chi square andmaximum likelihood, have been described in detail for the estimationof the parameters. The results of these two models are alsocompared with those of the probit model.     

The potential applications of cyanobacterial photosynthesis for clean technologies

Natural photosynthesis may be adapted to advantage in the development of clean energy technologies. Efficient biocatalysts that can be used in solar energy conversion technologies are the cyanobacteria. Photobioreactors incorporating cyanobacteria have been used to demonstrate (a) the production of hydrogen gas, (b) the assimilation of CO₂ with the production of algal biomass, (c) the excretion of ammonium, and (d) the removal of nitrate and phosphate from contaminated waters.Abbreviations Chl chlorophyll - DW dry weight - MSX L-methionine-D-L-sulphoximine - PAR photosynthetically active radiation - PU polyurethane - PV polyvinyl - PVC polyvinylchloride     

Genomic relationships in the genus Glycine (Fabaceae: Phaseoleae): use of a monoclonal antibody to the soybean Bowman-Blrk inhibitor as a genome marker

We investigated the use of a monoclonal antibody (MAb 238) to the soybean Bowman-Birk inhibitor (BBI) to verify and understand the intergenomic relationships among the wild perennial Glycine species. Competitive enzyme linked immunosorbent assay and western blot screening studies revealed that the accessions of B-genome (G. latifolia, G. microphylla, and G. tabacina, 2n = 40) and C-genome (G. curvata and G. cyrtoloba) species did not contain the MAb 238 crossreactive proteins (BBI-nulls). By contrast, all the A-genome (G. argyrea, G. canescens, G. clandestina, and G. latrobeana), E-genome (G. tomentella, 2n = 38), and F-genome (G. falcata) species, G. arenaria (genome unknown), and the polyploid (2n = 78,80) G. tomentella accessions were BBI-positive. The D-genome G. tomentella (2n = 40) and tetraploid G. tabacina (2n = 80) contained both BBI-null and BBI-positive type accessions. Among the recently described species, G. hirticaulis (2n = 40), G. lactovirens, and G. pindanica contained the MAb 238 crossreactive proteins while G. albicans did not. Glycine hirticaulis, G. pindanica, and G. tomentella (2n = 38) displayed highly similar MAb 238 crossreactive isoelectric focusing banding patterns, indicating that they are genomically close to each other. Glycine hirticaulis was found to have both diploid (2n = 40) and tetraploid (2n = 80) cytotypes. We demonstrated that the MAb 238 was specific to the trypsin inhibitor domain of the BBI. The MAb 238 clearly reflected all the previously established relationships in the genus Glycine, validating its use as a genome marker.     

Characterization of crystals of the thermostable DNA polymerase I from thermus aquaticus

Thermus aquaticus DNA polymerase I is an enzyme that is of both physiological and technological interest. It carries out template-directed polymerization of DNA at elevated temperatures and is widely used in polymerase chain reaction (PCR). We have obtained crystals of the enzyme that diffracts X-rays to at least 3.0 Å resolution in a cubic space group. Determination of the three-dimensional structure of the native enzyme along with those of relevant complexes will greatly enhance our knowledge of molecular events involved in DNA replication, will permit improvements in PCR, and will add to our knowledge of the structural bases of thermo stability in proteins. © 1995 Wiley-Liss, Inc.     

Movement and distribution pattern of the residues of granular insecticides in tropical soil and okra plants

Summary The increased downward mobility of phorate, quinalphos and carbofuran residues was detected in soil with increase in depth of soil column whereas aldicarb was found to remain localised mainly in 0–7.5 cm and 7.5–15.0 cm layers. Persistence of organophosphate insecticides was higher as compared to carbamates in all the soil layers. Residues of all the four insecticides got distributed in all parts of okra plant through uptake but accumulated in higher amounts in fruits only. Contribution No. 312/83 from I.I.H.R. Bangalore (India)     

A general multistate model for the analysis of hydrogen-exchange kinetics

In proton nmr, the chemical exchange rates of slowly exchanging labile hydrogens (with lifetimes in the range ～ 10 msec – ～ 1 sec) of peptides, proteins, and nucleic acids can be measured in H₂O by a combination of two separate experiments: (1) the transfer of solvent saturation and (2) saturation-recovery experiments. When these molecules exist in a dynamic equilibrium among different conformations, the experiments cannot be analyzed in a straightforward manner to derive the intrinsic exchange rates. In the present study we have derived analytical expressions for the above two experiments on a biomolecule under certain limiting conditions: (1) the extreme low-motility limit, where each of the conformational transitions is much slower than the corresponding hydrogen exchange rate with the solvent; (2) the high-motility limit (EX₂ mechanism), which is the opposite extreme of the previous limit; and (3) the low-motility limit (EX₁ mechanism), which is a mixture of limits (1) and (2), i.e., for some of the conformations, the exchange rate with the solvent is much faster than their conformational transition rates, while for the remaining conformations the reverse situation is realized. The results may be considered as a generalization to an arbitrary number of states of the two-state model treated by Hvidt. Equations have also been derived that are applicable to the iostope exchange method of measuring very slow exchange rates (with life-times of the order of minutes and longer) in biomolecules. The saturation recovery experiments performed in H₂O on the active pentapeptide fragment of thymopoietin serve to illustrate the high-motility limit. The theoretical formulation presented in this study can be easily adapted to other double-resonance techniques and also to situations where the kinetics of an arbitrary system existing in a multistate equilibrium are of interest.     

Synthesis of lysine-containing fragments of the Proteus mirabilis O27 O-specific polysaccharide and neoglycoconjugates therefrom.

Amide-linked lysine mono- and di-uronic acid fragments of the O-specific polysaccharide from P. mirabilis O27 have been synthesised. N epsilon-Boc-L-lysine tert-butyl ester was condensed with 2-azidoethyl glycosides of glucuronic acid and beta-D-GlcpNAc-(1----3)-beta-D-GlcpA. Transformation of the products into 2-acrylamidoethyl glycosides, followed by deprotection using trifluoroacetic acid, gave the target monomers that were converted into high-molecular-weight copolymer-type neoglycoconjugates.     

Identification and characterization of the enzymatic activity of zeta-crystallin from guinea pig lens. A novel NADPH:quinone oxidoreductase.

zeta-Crystallin is a major protein in the lens of certain mammals. In guinea pigs it comprises 10% of the total lens protein, and it has been shown that a mutation in the zeta-crystallin gene is associated with autosomal dominant congenital cataract. As with several other lens crystallins of limited phylogenetic distribution, zeta-crystallin has been characterized as an "enzyme/crystallin" based on its ability to reduce catalytically the electron acceptor 2,6-dichlorophenolindophenol. We report here that certain naturally occurring quinones are good substrates for the enzymatic activity of zeta-crystallin. Among the various quinones tested, the orthoquinones 1,2-naphthoquinone and 9,10-phenanthrenequinone were the best substrates whereas menadione, ubiquinone, 9,10-anthraquinone, vitamins K1 and K2 were inactive as substrates. This quinone reductase activity was NADPH specific and exhibited typical Michaelis-Menten kinetics. Activity was sensitive to heat and sulfhydryl reagents but was very stable on freezing. Dicumarol (Ki = 1.3 x 10(-5) M) and nitrofurantoin (Ki = 1.4 x 10(-5) M) inhibited the activity competitively with respect to the electron acceptor, quinone. NADPH protected the enzyme against inactivation caused by heat, N-ethylmaleimide, or H2O2. Electron paramagnetic resonance spectroscopy of the reaction products showed formation of a semiquinone radical. The enzyme activity was associated with O2 consumption, generation of O2- and H2O2, and reduction of ferricytochrome c. These properties indicate that the enzyme acts through a one-electron transfer process. The substrate specificity, reaction characteristics, and physicochemical properties of zeta-crystallin demonstrate that it is an active NADPH:quinone oxidoreductase distinct from quinone reductases described previously.     

Identification of nitroxide radioprotectors.

The nitroxide Tempol, a stable free radical, has recently been shown to protect mammalian cells against several forms of oxidative stress including radiation-induced cytotoxicity. To extend this observation, six additional water-soluble nitroxides with different structural features were evaluated for potential radioprotective properties using Chinese hamster V79 cells and clonogenic assays. Nitroxides (10 mM) were added 10 min prior to radiation exposure and full radiation dose-response curves were determined. In addition to Tempol, five of the six nitroxides afforded in vitro radioprotection. The best protectors were found to be the positively charged nitroxides, Tempamine and 3-aminomethyl-PROXYL, with protection factors of 2.3 and 2.4, respectively, compared with Tempol, which had a protection factor of 1.3. 3-Carboxy-PROXYL, a negatively charged nitroxide, provided minimal protection. DNA binding characteristics as studied by nonequilibrium dialysis of DNA with each of the nitroxides demonstrated that Tempamine and 3-amino-methyl-PROXYL bound more strongly to DNA than did Tempol. Since DNA is assumed to be the target of radiation-induced cytotoxicity, differences in protection may be explained by variabilities in affinity of the protector for the target. This study establishes nitroxides as a general class of new nonthiol radioprotectors and suggests other parameters that may be exploited to find even better nitroxide-induced radioprotection.     

Nuclear magnetic resonance and molecular modeling studies on O-beta-D-galactopyranosyl-(1----4)-O-beta-D-xylopyranosyl-(1----0)-L-se rine, a carbohydrate-protein linkage region fragment from connective tissue proteoglycans

The solution conformation of O-beta-D-galactopyranosyl-(1----4)-O-beta-D-xylopyranosyl-(1----0)-L-ser ine (GXS), a carbohydrate-protein linkage region fragment from connective tissue proteoglycans, was investigated by two-dimensional NMR spectroscopy and molecular modeling calculations. Specifically, the 1H and 13C resonances were assigned by 2D-COSY and by 1H-13C heteronuclear correlation spectroscopy methods. 2D-NOESY was used to generate distance constraints between the galactose and xylose and between the xylose and serine residues. The 1H vicinal coupling constants for the sugars and the serine were also determined. A general molecular modeling methodology suitable for complex carbohydrates was developed. This methodology employed molecular dynamics and energy minimization procedures together with the application of inter-residue spatial constraints across the linkages derived from 2D-NOESY. The first step in this methodology is the generation of a wide variety of starting conformations that span the (phi, psi) space for each linkage. In the present study, nine such conformations were constructed for each linkage using the torsion angles phi and psi corresponding to the gauche+, gauche-, and trans configurations across each of the two bonds constituting the linkage. These conformations were subjected to a combined molecular dynamics/energy minimization refinement using the NOESY derived constraints as pseudoenergy functions. Families of conformations for the whole molecule were then constructed from the structures derived for each linkage. Characterization of GXS using this methodology identified a single family of conformations that are consistent with the solution phase NMR data on this molecule.