Phytotoxicity of organic extracts of five medicinal plants of the Neotropical savanna.

Medicinal plants produce a high diversity of secondary metabolites with different biological activities, which are commonly evaluated when prospecting for bioherbicides. We analyzed the phytotoxic activity of organic extracts from the leaves of five medicinal species, Byrsonima intermedia, Moquiniastrum polymorphum, Luehea candicans, Miconia chamissois, and Qualea cordata. Phytotoxicity was evaluated on the initial growth of cucumber seedlings through tests with different concentrations of hexane, ethyl acetate, and methanol extracts. The results showed that all organic extracts and all concentrations affected cucumber development, with methanol extracts generally showing the greatest negative effect on the initial growth of the target species. The only exception was for M. chamissois extracts, in which the hexane extract had the greatest phytotoxicity. Furthermore, the organic extracts were subjected to preliminary phytochemical analysis, revealing the widespread presence of alkaloids along with other chemical classes. All the study species are thus potential candidates for use as natural herbicides.

Novel methods to estimate the enantiomeric ratio and the kinetic parameters of enantiospecific enzymatic reactions.

1The Enantiomeric Ratio (E) of the enzyme, acting as specific catalysts in resolution of enantiomers, is an important parameter in the quantitative description of these chiral resolution processes. In the present work, two novel methods hereby called Method I and II, for estimating E and the kinetic parameters Km and Vm of enantiomers were developed. These methods are based upon initial rate (v) measurements using different concentrations of enantiomeric mixtures (C) with several molar fractions of the substrate (x). Both methods were tested using simulated "experimental data" and actual experimental data. Method I is easier to use than Method II but requires that one of the enantiomers is available in pure form. Method II, besides not requiring the enantiomers in pure form shown better results, as indicated by the magnitude of the standard errors of estimates. The theoretical predictions were experimentally confirmed by using the oxidation of 2-butanol and 2-pentanol catalyzed by Thermoanaerobium brockii alcohol dehydrogenase as reaction models. The parameters E, Km and Vm were estimated by Methods I and II with precision and were not significantly different from those obtained experimentally by direct estimation of E from the kinetic parameters of each enantiomer available in pure form.

Resolution of DL-hydantoins by D-hydantoinase from Vigna angularis: production of highly enantioenriched N-carbamoyl-D-phenylglycine at 100% conversion.

D-Hydantoinase from Vigna angularis hydrolyzed rac-5-monosubstituted-hydantoins with polar and aromatic side chains and dihydrothymine but rac-5,5-disubstituted-hydantoins were not substrates of this enzyme. 5-Phenylhydantoin was the best substrate. By using this substrate, Ncarbamoyl-D-phenylglycine was obtained in quantitative yield and over 98% ee.

[General surgeon and breast reconstruction after mastectomy]. / Il chirurgo generale e la ricostruzione mammaria dopo mastectomia.

Breast reconstruction is widely used in patients who have undergone mastectomy for breast cancer. The paper underlines that reconstruction is often performed by the general surgeon who has become an expert in this type of plastic surgery. The Authors present their own clinical data, and describe the indications and techniques used, and the results obtained. In conclusion, it is stressed that ideally the same surgeon should be experienced in oncology and plastic surgery.

Inhibition of horse liver alcohol dehydrogenase and rabbit muscle lactate dehydrogenase by phenylhydrazine.

The activity of horse liver alcohol dehydrogenase was inhibited by phenylhydrazine. Kinetic experiments showed that this compound produced linear competitive inhibition with respect to NAD+ and linear noncompetitive inhibition with respect to ethanol. These results suggested that the inhibitor competes with NAD+ for the coenzyme binding site of alcohol dehydrogenase, forming a dead-end complex with the free form of the enzyme. A Ki value of 393 +/- 51 microM was estimated for the enzyme-inhibitor complex. Further evidence for this mechanism of inhibition arose from the fact that the same kind of inhibition was found for rabbit muscle lactate dehydrogenase. The Ki value for the lactate dehydrogenase-phenylhydrazine complex was 43.41 +/- 2.10 mM. The significant difference between these Ki values is explained in terms of known differences in hydrophobicity of the nicotinamide binding region in the two enzymes.

A microcomputer program for fitting two-substrate enzyme rate equations.

This paper describes a microcomputer program written in BASIC for fitting different two-substrate enzyme kinetic mechanisms. The present program is a complement of one which was recently published and was developed to fit different models of enzyme inhibition. The complete program resulting from this complementation allows the fitting of the most usual rate equations found in steady-state studies of enzyme kinetics. The program based on a non-linear least-squares regression, can be run on any microcomputer having the CP/M operating system. The initial rate equation for a steady-state random bisubstrate mechanism was chosen to evaluate the performance of the program, with contrived data of known error structure.

A microcomputer program for fitting enzyme inhibition rate equations.

This paper presents a computer program written in BASIC for fitting different enzyme inhibition kinetic models. The program, based on a nonlinear least-squares regression, can be run on any microcomputer with the CP/M operating system. Weighting of observed initial velocities is decided by the user by assessing constant variance, proportional variance or by incorporation of the variances calculated by a subroutine. The program also uses robust regression by bisquare weighting. All questions concerning data input, type of rate function, type of weight and the use of bisquare regression appear on the video display unit.

Pocket computer program for fitting the Hill equation.

This paper presents a program written in the BASIC language for the Radio Shack TRS-80 PC-1 or the Sharp PC 1211 pocket computers for fitting the Hill equation to experimental data. The program is based on a procedure involving a combination of an optimization technique and non-linear regression. The program determines precisely all three parameters of the Hill equation and in addition, it performs a simulation of the kinetic experiment using the parameter values previously estimated, calculating the sum of squares of residuals.

Pocket computer program for fitting the Michaelis-Menten equation.

This paper presents a program written for the Radio Shack TRS-80 or the Sharp PC 1211 pocket computers for fitting the Michaelis-Menten equation to experimental data by a non-linear regression analysis. The program determines the kinetic parameters Km and Vm, their standard errors and the residual standard error. In addition it performs a simulation of a kinetic experiment using the parameter values previously determined.

Application of a simple method to the characterization and differentiation of protein foods.

A screening method for the characterization and differentiation of proteinaceous samples and amino acid mixtures was applied to protein foods (4 protein-rich mixtures, one product sold as dietary supplement, and 3 raw materials of frequent use in the preparation of these products). Graphic profiles which describe the relative amounts of amino acid groups in the samples were obtained and subjected to statistical analysis. According to a previously established criterion of identity or difference, the correlation coefficients showed that at least 90% of the comparisons dealt with different samples. The method is proposed as a valuable tool for the quality control of protein-rich foods and their raw materials.

A screening method for protein characterization and differentiation.

A circular paper chromatographic method was developed for the separation of the amino acids in proteins into 7 subgroups. Butanol-acetic acid water (4+1+1) was used as the developing solvent. Eluted ninhydrin-stained aminograms gave rise to graphic profiles or numerical indexes based on absorbance percentages. The profiles can be used to compare protein-containing samples. Twenty different samples were studied through 190 comparisons of graphic profiles and coefficients of correlation, with only 4% misleading results. The method showed excellent reproducibility for the identification or differentiation of proteins and has the advantage of being performed with low-priced apparatus and reagents.