ABSTRACT
Ternary phase systems (water/surfactant/organic solvent) were utilised to increase and broaden the temperature optima of enzyme-catalysed reactions. Alcohol dehydrogenases from yeast and Thermoanaerobium brockii (EC 1.1.1.1 and EC 1.1.1.2), lactate dehydrogenase from Lactobacillus delbrueckii (EC 1.1.1.28) and the particulate hydrogenase from Ralstonia eutropha (EC 1.18.99.1) were used as model enzymes in microemulsions, consisting of the surfactant Aerosol OT, and various alkane solvent and aqueous phases. All enzymes exhibited, besides an increase in specific activity, an upshift of the temperature optimum of the catalysed reaction. The temperature optimum could be further shifted by variation of the chain length of the solvent used and/or the addition of compatible solutes to the aqueous phase. Under optimised conditions, catalytic reactions of enzymes from mesophilic microorganisms had temperature optima in the range generally obtained with enzymes from thermophilic organisms.
Subject(s)
Alcohol Dehydrogenase/metabolism , Hydrogenase/metabolism , L-Lactate Dehydrogenase/metabolism , Alkanes/chemistry , Catalysis , Dioctyl Sulfosuccinic Acid/chemistry , Emulsions , Enzyme Stability , Gram-Positive Bacteria/enzymology , Ralstonia/enzymology , Saccharomyces cerevisiae/enzymology , Temperature , Water/chemistryABSTRACT
Electron microscopic immunogold labeling experiments were performed with ultrathin sections of plasmolyzed cells of Alcaligenes eutrophus and "whole-mount" samples of spheroplasts and protoplasts. They demonstrated that antigenic determinants of the membrane-bound hydrogenase are exposed, at the outside of the cytoplasmic membrane, to the periplasm.
