Kinetics of pressure-induced inactivation of bovine liver glutamate dehydrogenase

Intrinsic fluorescence spectroscopy of glutamate dehydrogenase: Integrated behavior and deconvolution analysis

In this paper, we present a deconvolution method aimed at spectrally resolving the broad fluorescence spectra of proteins, namely, of the enzyme bovine liver glutamate dehydrogenase (GDH). The analytical procedure is based on the deconvolution of the emission spectra into three distinct Gaussian fluorescing bands G(j). The relative changes of the G(j) parameters are directly related to the conformational changes of the enzyme, and provide interesting information about the fluorescence dynamics of the individual emitting contributions. Our deconvolution method results in an excellent fitting of all the spectra obtained with GDH in a number of experimental conditions (various conformational states of the protein) and describes very well the dynamics of a variety of phenomena, such as the dependence of hexamers association on protein concentration, the dynamics of thermal denaturation, and the interaction process between the enzyme and external quenchers. The investigation was carried out by means of different optical experiments, i.e., native enzyme fluorescence, thermal-induced unfolding, and fluorescence quenching studies, utilizing both the analysis of the "average" behavior of the enzyme and the proposed deconvolution approach.

Effects of temperature and pressure on Rhizomucor miehei lipase stability

Both high temperature and high hydrostatic pressure induce irreversible deactivation of enzymes. They enable the enzyme's thermodynamic parameters to be determined and are used to study the mechanisms involved in biochemical systems. The effect of these two factors on the stability of Rhizomucor miehei lipase have been investigated. The stability criterion used was residual hydrolytic activity of the lipase. Experimental and theoretical parameters, obtained by linear regression analysis, were compared with theoretical kinetics in order to validate the series-type inactivation model. The lipase of R. miehei was deactivated by either thermal or pressure treatment. Moreover conformational studies made by fluorescence spectroscopy suggest that the conformational changes induced by pressure were different from those induced by temperature. In addition they show that after thermal deactivation there were less intermolecular hydrogen bonded structures formed than was the case for deactivation by high pressure.

Optical characterization of glutamate dehydrogenase monolayers chemisorbed on SiO2

This paper describes the formation of glutamate dehydrogenase monolayers on silicon dioxide, and their characterization by means of physical techniques, i.e., fluorescence spectroscopy and Fourier-transform infrared spectroscopy. Detailed investigations of the intrinsic stability of native proteins in solution were carried out to elucidate the occurrence of conformational changes induced by the immobilization procedure. The enzyme monolayers were deposited on SiO2 after preexposing silicon surfaces to 3-aminopropyltriethoxysilane and reacting the silylated surfaces with glutaric dialdehyde. The optical characterization demonstrates that the immobilization does not interfere with the fold pattern of the native enzyme. In addition, fluorescence spectroscopy, thermal denaturation, and quenching studies performed on the enzyme in solution well describe the folding and unfolding properties of glutamate dehydrogenase. The photophysical studies reported here are relevant for nanobioelectronics applications requiring protein immobilization on a chip.

L-Glutamate dehydrogenase from the antarctic fish Chaenocephalus aceratus. Primary structure, function and thermodynamic characterisation: relationship with cold adaptation

In order to study the molecular mechanisms of enzyme cold adaptation, direct amino acid sequence, catalytic features, thermal stability and thermodynamics of the reaction and of heat inactivation of L-glutamate dehydrogenase (GDH) from the liver of the Antarctic fish Chaenocephalus aceratus (suborder Notothenioidei, family Channichthyidae) were investigated. The enzyme shows dual coenzyme specificity, is inhibited by GTP and the forward reaction is activated by ADP and ATP. The complete primary structure of C. aceratus GDH has been established; it is the first amino acid sequence of a fish GDH to be described. In comparison with homologous mesophilic enzymes, the amino acid substitutions suggest a less compact molecular structure with a reduced number of salt bridges. Functional characterisation indicates efficient compensation of Q(10), achieved by increased k(cat) and modulation of S(0.5), which produce a catalytic efficiency at low temperature very similar to that of bovine GDH at its physiological temperature. The structural and functional characteristics are indicative of a high extent of protein flexibility. This property seems to find correspondence in the heat inactivation of Antarctic and bovine enzymes, which are inactivated at very similar temperature, but with different thermodynamics.

Irreversible high pressure inactivation of beta-galactosidase from Kluyveromyces lactis: comparison with thermal inactivation

High hydrostatic pressure and high temperature are both shown to induce inactivation of Kluyveromyces lactis beta-galactosidase in deionised water and their respective effects are compared. These two physical parameters lead to similar inactivation kinetics which can be suitably represented by series-type models. The plot of half-lives as a function of pressure is close to the same plot towards temperature. Thus, the same inactivation rate constant can be obtained in two different ways: an increase in pressure at room temperature or an increase in temperature at atmospheric pressure (e.g. 125 MPa at 25 degrees C or 45 degrees C at 0.1 MPa for a kappa 1 value about 28 x 10(-2) min -1). When beta-galactosidase was prepared in 0.1 M potassium phosphate buffer pH 7.3, its stability in extreme conditions of pressure as at high temperature was strongly enhanced. This stabilizing effect of the buffer was essentially attributed to a pH-effect by comparison with the behaviour of the enzyme in a similar buffer but with a 10-fold lower ionic strength.

Effect of temperature and pressure on yeast invertase stability: a kinetic and conformational study

Kinetics of the temperature- or pressure-induced denaturation of invertase from Saccharomyces cerevisiae were obtained in the temperature range 45-70 degrees C and in the pressure range 500-650 MPa. The investigation was done by measuring the residual activities after cooling or pressure release and the intrinsic fluorescence of aromatic amino-acids (tyrosine and tryptophan) upon excitation at 277 nm. The residual activity decreased exponentially as a function of time incubation according to a biphasic model either with pressure or temperature, whereas the fluorescence emission indicated a difference between these two parameters. When the enzyme was subjected to thermal treatment, the fluorescence of tyrosine and tryptophan decreased slowly, while after high-pressure treatment, these aromatic residues become more exposed to the aqueous solvent during unfolding, giving rise to a large decrease in fluorescence in the 330-340 nm region. Moreover, in the latter case, an enhancement of light scattering intensity showed changes in protein-protein interactions.