Annals of the New York Academy of SciencesVolume 613, Issue 1 p. 506-510 Kinetic Indication for a Conformational Change of Enzyme by a Modified Aqueous Microenvironment ZU FENG XU, ZU FENG XU Laboratoire de Technologie Enzymatique Université de Compiègne 60206 Compiègne, FranceSearch for more papers by this authorDANIEL THOMAS, DANIEL THOMAS Laboratoire de Technologie Enzymatique Université de Compiègne 60206 Compiègne, FranceSearch for more papers by this authorVÉRONIQUE LARRETA-GARDE, Corresponding Author VÉRONIQUE LARRETA-GARDE Laboratoire de Technologie Enzymatique Université de Compiègne 60206 Compiègne, FranceTo whom all correspondence should be addressed.Search for more papers by this author ZU FENG XU, ZU FENG XU Laboratoire de Technologie Enzymatique Université de Compiègne 60206 Compiègne, FranceSearch for more papers by this authorDANIEL THOMAS, DANIEL THOMAS Laboratoire de Technologie Enzymatique Université de Compiègne 60206 Compiègne, FranceSearch for more papers by this authorVÉRONIQUE LARRETA-GARDE, Corresponding Author VÉRONIQUE LARRETA-GARDE Laboratoire de Technologie Enzymatique Université de Compiègne 60206 Compiègne, FranceTo whom all correspondence should be addressed.Search for more papers by this author First published: December 1990 https://doi.org/10.1111/j.1749-6632.1990.tb18209.xCitations: 9AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Citing Literature Volume613, Issue1Enzyme Engineering 10December 1990Pages 506-510 RelatedInformation

Sorbitol, added as a depressor of water activity in the reaction medium of yADH, can modify the kinetic behaviour of the enzyme towards the four substrates tested: ethanol, propanol, butanol and pentanol, as well as towards the coenzyme NAD. All apparent Km values of the alcohol substrates and NAD decreased as the additive concentration increased. However, the additive-caused modifications of the enzyme activity were found to depend on the carbon-chain length of the alcohol substrate, in other words, the catalytic selectivity of the enzyme towards different substrates was changed by the additive. These results and supplementary experiments suggested that sorbitol may have two opposing effects on the enzyme: the positive effect leads the enzyme to adopt a conformation which is more accessible to its substrates; while the negative effect results in a diffusional constraint for the enzyme reaction. Observed results were the combination of the two opposing effects.

The complete primary structure of thioredoxin from Rhodobacter sphaeroides Y has been determined by analysis of peptides after cleavage with cyanogen bromide, chymotrypsin and trypsin. Peptides were separated by HPLC and analyzed by liquid-phase and gas-phase sequencer degradations. The protein consists of 105 residues (Mr = 11,180); its amino acid sequence shows a clear homology to the five known thioredoxins from plant or bacterial sources, with 40-56% residue identity when the proteins are aligned at the active-site disulfide. Not only the active-site regions are conserved, but also residues which belong to the hydrophobic surface suggested to be important for binding of procaryote thioredoxins in redox interactions with other proteins (residues 75-76; 91-93 in Escherichia coli). A three-dimensional model of Rb. sphaeroides thioredoxin has been derived from the E. coli crystallographic structure with computer graphics. This model indicates that the overall structures as well as the active sites are closely similar; however, the residue substitutions allow both proteins to adopt different local folding as shown in the hydrophobic core.

Electron carrier proteins from Desulfovibrio sp., especially flavodoxins, have been tested as electron mediator between spinach chloroplast membranes and hydrogenase from aerobic hydrogen-oxidizing bacteria. Due to the slow electron transfer between flavodoxin and hydrogenase the rate of hydrogen production is low.

Immobilization of lettuce (Lactuca sativa) thylakoids has been performed by using glutaraldehyde and bovine serum albumin. Confirming previous reports, a stabilization of the O(2) evolution activity of the photosystem II (PSII) under storage and functional conditions has been observed. The present work is devoted to the role played by mono-and divalent cations, during the immobilization process itself, on the O(2) production. Four types of measurements have been employed: kinetic measurements, low temperature (77 K) fluorescence emission, photoacoustic (PA) spectroscopy, and electron microscopy observations. We show that the effect of glutaraldehyde is complex because it acts as an inhibitor, a stabilizing agent, and a cross-linking reactive. In the present studies, the thylakoids are immobilized within a polymeric insoluble albumin matrix. The highest activity yield and the best storage conditions are obtained when 0.15 mm Na(+) (or K(+)), 1 mm Mg(2+), and 0.1 mm Mn(2+) are present in the resuspending media before the immobilization. Due to modifications of the ionic content during such a process, structural differences are observed on the stacking degree of thylakoids. No modification of the fluorescence and PA spectra after the immobilization are found. Furthermore, a correlation between activities and spectral changes have been shown: when the activities increase, the F(735) to F(695) ratio increases and the PA(676) to PA(440) ratio decreases.