Mathematical analysis of competition between sensory ganglion cells for neurotrophic factor in the skin

A model is presented of competition between sensory axons for trophic molecules (e.g. a neurotrophin such as NGF), produced in a region of skin small enough to permit their free diffusion throughout it; e.g., a touch dome, or a vibrissal follicle hair sinus. The variables specified are the number of high affinity trophic factor receptors per axon terminal and the concentration of trophic factor in the extracellular space. Previous models of this class predicted the loss of all the axons innervating the region except the one requiring least trophic factor for its maintenance, even with high rates of trophic factor production. In the present model, we have imposed upper limits to axonal growth, thereby introducing new equilibria, and we show by a global analysis using LaSalle's theorem, and also by local analysis, that several axons can then coexist if the rate of production of trophic molecules is sufficiently high.     

Characterization of the surfactin synthetase C-terminal thioesterase domain as a cyclic depsipeptide synthase

The C-terminal thioesterase domain of the nonribosomal peptide synthetase producing the lipopetide surfactin (Srf TE) retains autonomous ability to generate the cyclic peptidolactone skeleton of surfactin when provided with a soluble beta-hydroxy-butyryl-heptapeptidyl thioester substrate. Utilizing the recently solved crystal structure [Bruner, S. D., et al. (2002) Structure 10, 301-310], the active-site nucleophile, Ser80, was changed to Cys, and the other members of the catalytic triad, Asp107 and His207, were changed to Ala, with the resulting mutants lacking detectable activity. Two cationic side chains in the active site, Lys111 and Arg120, were changed to Ala, causing an increased partitioning of the product to hydrolysis, as did a P26G mutant, mimicking the behavior of lipases. To evaluate recognition elements in substrates used by Srf TE, alterations to the fatty acyl group, the heptapeptide, and the thioester leaving group were made, and the resulting substrates were characterized for kinetic competency and flux of product to cyclization or hydrolysis. Alterations that could be accepted for cyclization were identified in all three parts of the substrate, although tolerance limits for changes varied. In addition, cocrystal structures of Srf TE with dipeptidyl boronate inhibitors were solved, illustrating the critical binding determinants of the substrate. On the basis of the structures and biochemical data, the cyclizing conformation of the surfactin peptide was modeled into the enzyme active site.     

Expression of an engineered cysteine proteinase inhibitor (Oryzacystatin-IΔD86) for nematode resistance in transgenic rice plants

 We have used a genotype-independent transformation system involving particle gun bombardment of immature embryos to genetically engineer rice as part of a programme to develop resistance to nematodes. Efficient tissue culture, regeneration, DNA delivery and selection methodologies have been established for elite African varieties (‘ITA212’, ‘IDSA6’, ‘LAC23’, ‘WAB56-104’). Twenty-five transformed clones containing genes coding for an engineered cysteine proteinase inhibitor (oryzacystatin-IΔD86, OC-IΔD86), hygromycin resistance (aphIV) and β-glucuronidase (gusA) were recovered from the four varieties. Transformed plants were regenerated from all clones and analysed by PCR, Southern and western blot. Detectable levels of OC-IΔD86 (up to 0.2% total soluble protein) in plant roots were measured in 12 out of 25 transformed rice lines. This level of expression resulted in a significant 55% reduction in egg production by Meloidogyne incognita. Received: 4 August 1997 / Accepted: 22 August 1997     

Purification of catalytically active hepatic NADPH cytochrome P450 oxidoreductase from the rhesus monkey, Macaca mulatta.

Hepatic NADPH cytochrome P450 oxidoreductase capable of supporting polysubstrate monooxygenase (PSMO) reactions was purified from microsomes obtained from phenobarbitone (PB) pretreated rhesus monkey. Two preparations of the enzyme purified by affinity and molecular exclusion chromatographic techniques demonstrated specific content of 19.5 and 37.9 nmol cytochrome c reduced/min/mg protein and subunit molecular weight of 66 and 80 kDa, respectively. Both forms supported oxidation of NADPH and reduction of cytochrome c and DCIP but only 80 kDa preparation supported PSMO reactions. The reconstituted system consisted of hepatic P450, NADPH cytochrome P450 oxidoreductase, cytochrome b5 all purified from PB pretreated rhesus monkey and dilauroyl phosphatidylcholine or microsomal lipid. Eighty kDa preparation supported the metabolism of aminopyrine and tolbutamide by hepatic P4502C and erythromycin, ethylmorphine and nifedipine by hepatic P450 3A, respectively. The turnover of these substrates increased in the presence of partially purified cytochrome b5 from the rhesus monkey. To best of our knowledge this is the first report on the purification of monkey hepatic NADPH cytochrome P450 oxidoreductase capable of supporting in vitro PSMO by different isozymes of P450.     

A mathematical model to predict the tissue response to parthenin — An allelochemical

Parthenin — a sesquiterpene lactone fromParthenium hysterophorus L. is an allelochemical that prevents the germination ofPhaseolus aureus Roxb. cv. ML-5 seeds. The response of the seed has been attributed to the inhibition of the respiratory electron transport ability of its embryo. It has been shown to depend directly not only upon concentration of parthenin, but simultaneously on the duration of exposure of the seeds to the chemical as well. A strong correlation exists between the quantum of the response and the product of the period of exposure and the concentration of parthenin. In order to predict the maximum possible germination ability of the seed exposed for a given period to a given concentration of parthenin, an expression X = 10000 Y³ / [e^Y/0.31-1] was formulated from the equation X = AY³/[e^Y/Y0-1], where X represents values of maximum respiratory activity, Y represents the product of concentration and time in units mg cn^-3 h, A represents a dimensional constant. The trend and nature of response that is calculated on the basis of formulation coincides with that of measured response through spectrophotometry.     

The metabolism of higher chlorinated benzene isomers.

The metabolism of the isomeric tri- and tetrachlorobenzene isomers, penta- and hexachlorobenzene was investigated in the rabbit. The major urinary metabolites of the isomeric tri- and tetrachlorobenzenes were identified as the corresponding tri- and tetrachlorophenols whose structures were confirmed by chromatographic analyses. The genesis of the formation of metabolites is discussed in terms of their possible arene oxide intermediates in which the NIH shift of a chlorine atom is observed in the oxidation of many of the isomers. Pentachlorobenzene is metabolized to give both pentachlorophenol and a dechlorination-hydroxylation product which was identified as 2,3,4,5-tetrachlorophenol. The hexachlorobenzene substrate did not give any phenolic metabolites.     

Microwave absorption by folded DNA chains

Absorption of radiation by DNA polymer is calculated for the case of bent polymer chains. The molecule is assumed to be straight except for localized bends. The region between two bends is studied in particular. The vibrational properties of the bends are parameterized by a transmission and a reflection coefficient. A general Green function expression for absorption is studied for various values of the damping rate, as well as the transmission/reflection coefficients. Curves of absorption vs frequency are shown for a number of cases.     

Application of calcium alginate immobilized and crude pectin lyase from Bacillus cereus in degumming of plant fibres

Abstract

In this study, the purified pectin lyase was immobilized in calcium alginate beads and compared with crude enzyme for application in degumming of buel and banana plant fibres. From the data of scanning electron microscopy (SEM), it was observed that untreated buel fibres were covered by non-cellulosic materials (pectin, hemicelluloses and waxes) and the surface of enzymatically treated buel fibres looked smoother. Also, the crude alkaline pectin lyase treated buel fibre exhibited a considerably cleaner surface, which suggested that the crude pectin lyase could provide better degumming effects in comparison to the immobilized pectin lyase. In case of banana fibre, the FTIR spectroscopy showed that both crude and immobilized alkaline pectin lyase treatments of banana plant fibres were equally efficient in degumming. The enzymatic degumming of buel and banana with crude pectin lyase resulted in maximum release of galacturonide after 24?h for buel and 15?h for banana fibre. The optimum temperature for degumming of buel and banana fibres with crude pectin lyase was found to be 50?°C and 45?°C, respectively. Also, the maximum galacturonide was released with 200 and 250?U of pectin lyase for buel and banana fibre, respectively.