Investigation of behavior of an enzyme in a biphasic system: soybean lipoxygenase-1.

Soybean lipoxygenase-1 (EC 1.13.11.12) reaction with linoleic acid as substrate was used to study the biocatalysis in a biphasic system when the reactants have surface-active properties. The poorly water-soluble substrate was initially dissolved in an apolar solvent (octane). The hydroperoxide produced was water soluble and remained in the aqueous phase (borate buffer). The bioreactor was a modified Lewis cell with a well-defined interfacial area between the two phases. Two phenomena were studied separately: the reactant transfer between the two phases and the biocatalyzed reaction in an aqueous medium. This allowed determination of the transfer and the reaction constants. Substrate transfer was found to be affected by the progress of the reaction, because linoleic acid and the hydroperoxy acid have an influence on the interfacial tension. Inactivation of the biocatalyst at the interface was observed in the bioreactor. These results indicate that it is impossible to analyze the system behavior with the method proposed in the literature, which is based on the sequential study of the substrate transfer to the aqueous phase and its biocatalysis by lipoxygenase. The interaction between transfer phenomena and reaction kinetics was studied in the biphasic system. The kinetics were different from those obtained in the aqueous medium. Catalysis and transfer influence each other reciprocally. In this compartmentalized system, cooperativity phenomena were obtained using a nonallosteric enzyme. The evolution of the system was modeled (Runge-Kutta algorithm). The curves obtained were very close to those determined experimentally.

Enzymatic synthesis of alkyl beta-D-xylosides by transxylosylation and reverse hydrolysis.

The Trichoderma reesei beta-xylosidase (EC 3.2.1.37) is used to catalyze the production of alkyl beta-D-xyloside. Two general methods of production are tested and compared using the same enzyme: transglycosylation and reverse hydrolysis. Using both methods, primary, secondary, and tertiary alcohols are studied as acceptors. In kinetically controlled process (transglycosylation), the chosen donor is methyl beta-D-xyloside and primary, secondary, and tertiary alkyl alcohols are accepted. In the equilibrium-controlled synthesis, the donor is xylose whereas acceptors are only primary and secondary alcohols. The influence of the donor concentration is investigated in both processes. The yields of the kinetically controlled reactions are higher compared with those of the equilibrium-controlled synthesis. The specificity of the beta linkage is confirmed by proton nuclear magnetic resonance ((1)H NMR) analysis. (c) 1994 John Wiley & Sons, Inc.

Geographic variation in the prevalence of Raynaud's phenomenon: Charleston, SC, USA, vs Tarentaise, Savoie, France.

We estimated the prevalence of Raynaud's phenomenon (RP) in the general population of 2 geographic areas, Charleston County, South Carolina, USA, and Tarentaise, Savoie, France, using the same methodology in both countries. The first phase of the study, consisting of the telephone survey of a randomly drawn sample of households, yielded 2086 completed interviews in Charleston and 2000 in Tarentaise. Cold sensitivity or unusual digital color changes were reported by 17.9% of the subjects in Charleston and by 31.3% in Tarentaise. In the second phase of the study the diagnosis of RP was made by a medical team. Based on these results, the estimated prevalence of RP is 5.0% (0.8% SE) in Charleston (women 5.7%, men 4.3%) and 16.8% (2.0% SE) in Tarentaise (women 20.1%, men 13.5%).