Pressure dependence of thermolysin catalysis

Extremophile Microbial Communities and Enzymes for Bioenergetic Application Based on Multi-Omics Tools

Abstract: Genomic and proteomic advances in extremophile microorganism studies are increasingly demonstrating their ability to produce a variety of enzymes capable of converting biomass into bioenergy. Such microorganisms are found in environments with nutritional restrictions, anaerobic environments, high salinity, varying pH conditions and extreme natural environments such as hydrothermal vents, soda lakes, and Antarctic sediments. As extremophile microorganisms and their enzymes are found in widely disparate locations, they generate new possibilities and opportunities to explore biotechnological prospecting, including biofuels (biogas, hydrogen and ethanol) with an aim toward using multi-omics tools that shed light on biotechnological breakthroughs.

Mesophilic Pyrophosphatase Function at High Temperature: A Molecular Dynamics Simulation Study

The mesophilic inorganic pyrophosphatase from Escherichia coli (EcPPase) retains function at 353 K, the physiological temperature of hyperthermophilic Thermococcus thioreducens, whereas the homolog protein (TtPPase) from this hyperthermophilic organism cannot function at room temperature. To explain this asymmetric behavior, we examined structural and dynamical properties of the two proteins using molecular dynamics simulations. The global flexibility of TtPPase is significantly higher than its mesophilic homolog at all tested temperature/pressure conditions. However, at 353 K, EcPPase reduces its solvent-exposed surface area and increases subunit compaction while maintaining flexibility in its catalytic pocket. In contrast, TtPPase lacks this adaptability and has increased rigidity and reduced protein/water interactions in its catalytic pocket at room temperature, providing a plausible explanation for its inactivity near room temperature.

Effects of hydrostatic pressure on the quaternary structure and enzymatic activity of a large peptidase complex from Pyrococcus horikoshii

While molecular adaptation to high temperature has been extensively studied, the effect of hydrostatic pressure on protein structure and enzymatic activity is still poorly understood. We have studied the influence of pressure on both the quaternary structure and enzymatic activity of the dodecameric TET3 peptidase from Pyrococcus horikoshii. Small angle X-ray scattering (SAXS) revealed a high robustness of the oligomer under high pressure of up to 300 MPa at 25°C as well as at 90°C. The enzymatic activity of TET3 was enhanced by pressure up to 180 MPa. From the pressure behavior of the different rate-constants we have determined the volume changes associated with substrate binding and catalysis. Based on these results we propose that a change in the rate-limiting step occurs around 180 MPa.

Characterization of commercial amylases for the removal of filter cake on petroleum wells

Drilling fluid has many functions, such as carry cuttings from the hole permitting their separation at the surface, cool and clean the bit, reduce friction between the drill pipe and wellbore, maintain the stability of the wellbore, and prevent the inflow of fluids from the wellbore and form a thin, low-permeable filter cake. Filter cake removal is an important step concerning both production and injection in wells, mainly concerning horizontal completion. The drilling fluids are typically comprised of starch, the most important component of the filter cake. A common approach to remove this filter cake is the use of acid solutions. However, these are non-specific reactants. A possible alternative is the use of enzymatic preparations, like amylases, that are able to hydrolyze starch. Wells usually operate in drastic conditions for enzymatic preparations, such as high temperature, high salt concentration, and high pressure. Thus, the main objective of this work was to characterize four enzymatic preparations for filter cake removal under open hole conditions. The results showed that high salt concentrations (204,000 ppm NaCl) in completion fluid decreased amylolytic activity. All enzymatic preparations were able to catalyze starch hydrolysis at all temperatures tested (30, 65, 80, and 95 degrees C). An increase of amylolytic activity was observed with the increase of pressure (100, 500 and 1,000 psi) for one commercial amylase.

Effect of temperature and pressure on the proteolytic specificity of the recombinant 20S proteasome from Methanococcus jannaschii

The hydrolytic specificity of the recombinant 20S proteasome from the deep-sea thermophile Methanococcus jannaschii was evaluated toward oxidized insulin B-chain across a range of temperatures (35 degrees, 55 degrees, 75 degrees, and 90 degrees C) and hydrostatic pressures (1, 250, 500, and 1,000 atm). Of the four temperatures considered, the same maximum overall hydrolysis rate was observed at both 55 degrees and 75 degrees C, which are much lower than the T(opt) of 116 degrees C previously observed for a small amide substrate (Michels and Clark 1997). At 35 degrees C the rates of cleavage were highest at the carboxyl side of glutamine and leucine, whereas at the three higher temperatures, the most rapid cleavages occurred after leucine and glutamic acid residues. The distribution of proteolytic fragments and the cleavage sequence also varied between the lowest and higher temperatures. Application of hydrostatic pressure did not increase proteasome activity, as observed previously for the amide substrate (Michels and Clark 1997), but instead significantly reduced the overall conversion of the polypeptide substrate. Overall cleavage patterns observed for the recombinant M. jannaschii proteasome were similar to those reported previously for Thermoplasma acidophilum (Akopian et al. 1997) and human proteasomes (Dick et al. 1991), indicating that proteasome specificity has been conserved despite significant environmental diversity.

Pressure effects on intra- and intermolecular interactions within proteins

The effects of pressure on protein structure and function can vary dramatically depending on the magnitude of the pressure, the reaction mechanism (in the case of enzymes), and the overall balance of forces responsible for maintaining the protein's structure. Interactions between the protein and solvent are also critical in determining the response of a protein to pressure. Pressure has long been recognized as a potential denaturant of proteins, often promoting the disruption of multimeric proteins, but recently examples of pressure-induced stabilization have also been reported. These global effects can be explained in terms of pressure effects on individual molecular interactions within proteins, including hydrophobic, electrostatic, and van der Waals interactions, which can now be studied in greater detail than ever before. However, many uncertainties remain, and thorough descriptions of how proteins respond to pressure remain elusive. This review summarizes basic concepts and new findings related to pressure effects on intra- and intermolecular interactions within proteins and protein complexes, and discusses their implications for protein structure-function relationships under pressure.

Cold denaturation of proteins under high pressure

The advantageous usage of the high pressure technique in studies of cold denaturation of proteins is reviewed, with a brief explanation of the theoretical background of this universal phenomenon. Various experimental results are presented and discussed, explaining the plausible image of the cold denatured state of proteins. In order to understand more clearly this phenomenon and protein structure transition in general, several studies on model polymer systems are also reviewed.

Activity and stability of a neutral protease from Vibrio sp. (vimelysin) in a pressure-temperature gradient

The apparent second-order rate constant of hydrolysis of Fua-Gly-LeuNH2 by vimelysin, a neutral protease from Vibrio sp. T1800, was measured in a variable pressure-temperature gradient (0. 1-400 MPa and 5-40 degrees C). The apparent maximum rate was observed at approximately 15 degrees C and 150-200 MPa; the pressure-activation ratio (kcat/Km(max)/kcat/Km(0.1 MPa)) was reached about sevenfold. The pressure dependence of the kcat and Km parameters at constant temperature (25 degrees C) revealed that the pressure-activation below 200 MPa was mainly caused by a change in the kcat parameter. The change in the intrinsic fluorescence intensity of vimelysin was also measured in a pressure-temperature plane (0.1-400 MPa and -20 to +60 degrees C). The fluorescence intensity was found to decrease by increasing pressure and temperature, and the isointensity contours were more or less circular. The tangential lines to the contours at high temperatures and low to medium pressures seem to have slightly positive slopes, which was reflected by the higher residual activities left after incubations at higher temperatures and medium pressure (200 MPa and 50 degrees C) and by the almost intact secondary structure left after 1 h of incubation at 200 MPa and 40 degrees C, as studied by circular dichroism. These results were compared with the corresponding results for thermolysin, a moderately thermostable protease from Bacillus thermoproteolyticus. Apparent differences that might be related to the temperature adaptations of the respective source microbes are also discussed.

Single-point amino acid substitutions at the 119th residue of thermolysin and their pressure-induced activation

The effect of amino acid substitution at the 119th site of thermolysin (TLN) on the pressure activation behavior of this enzyme was studied for four mutants at pressures < 300 MPa. For Q119Q, Q119N and Q119R, the highest activation was observed to be over 30 times that at atmospheric pressure and the activation volumes (deltaV++) were about -75 ml/mol. However, we obtained only 10 times higher activation for Q119E and Q119D (deltaV++ approximately -60 ml/mol). The intrinsic fluorescence of TLN changed at pressures > 300 MPa, and the latter two mutants showed a smaller deltaGapp and deltaVapp of transition than the wild type. These results are discussed with respect to the hydration change in the enzyme protein around the substituted region.

Fluorescence and FTIR study of the pressure-induced denaturation of bovine pancreas trypsin

The pressure denaturation of trypsin from bovine pancreas was investigated by fluorescence spectroscopy in the pressure range 0. 1-700 MPa and by FTIR spectroscopy up to 1000 MPa. The tryptophan fluorescence measurements indicated that at pH 3.0 and 0 degrees C the pressure denaturation of trypsin is reversible but with a large hysteresis in the renaturation profile. The standard volume changes upon denaturation and renaturation are -78 mL.mol-1 and +73 mL.mol-1, respectively. However, the free energy calculated from the data in the compression and decompression directions are quite different in absolute values with + 36.6 kJ.mol-1 for the denaturation and -5 kJ. mol-1 for the renaturation. For the pressure denaturation at pH 7.3 the tryptophan fluorescence measurement and enzymatic activity assays indicated that the pressure denaturation of trypsin is irreversible. Interestingly, the study on 8-anilinonaphthalene-1-sulfonate (ANS) binding to trypsin under pressure leads to the opposite conclusion that the denaturation is reversible. FTIR spectroscopy was used to follow the changes in secondary structure. The pressure stability data found by fluorescence measurements are confirmed but the denaturation was irreversible at low and high pH in the FTIR investigation. These findings confirm that the trypsin molecule has two domains: one is related to the enzyme active site and the tryptophan residues; the other is related to the ANS binding. This is in agreement with the study on urea unfolding of trypsin and the knowledge of the molecular structure of trypsin.

Effect of high hydrostatic pressure on the porin OmpC from Escherichia coli

Porin OmpC from Escherichia coli was reconstituted in liposomes and its gating kinetics were recorded at high hydrostatic pressure, up to 90 MPa, using a development of the patch clamp technique. The composition of the recording solution influenced the results but generally high hydrostatic pressure favoured channel opening.

Studies on the formation and stability of a complex between Streptomyces proteinaceous metalloprotease inhibitor and thermolysin

The effects of certain physicochemical parameters on the formation and stability of a complex between Streptomyces proteinaceous metalloprotease inhibitor (SMPI) and thermolysin were investigated. SMPI had its lowest Ki value at a pH of around 6.5 (similar to the pH dependence of the kcat/K(m) of thermolysin catalysis), reflecting the splitting mechanism of the SMPI inhibition of thermolysin. This Ki increased with an increase in pressure, and in (Ki-1) was almost linear with respect to pressure. The volume of the reaction (delta Vcomp), which is the volume change accompanying enzyme-inhibitor complex formation, was calculated as +8.1 +/- 0.3 mL.mol-1, which has a sign opposite to delta Vcomp for neutral peptide inhibitors and acyl-peptide substrates. The temperature dependence of Ki-1 gave the reaction enthalpy (delta Hcomp) and reaction entropy (delta Scomp) of the complex formation as 34.6 +/- 1.4 kJ.mol-1 and 298 +/- 5 J.mol-1.K-1, respectively. These positive reaction volumes and reaction entropies were related to the electrostatic interactions and ionic strength dependence of Ki which corresponded to the key ionic interaction during complex formation. Complex formation with SMPI stabilized thermolysin against pressure perturbation as observed by the changes in the Trp fluorescence of thermolysin with increasing pressure. Thermal stability, however, was affected very little by complex formation with SMPI. Phosphoramidon, Cbz-Phe-Gly-NH2 and Cbz-Phe also positively affected the pressure-tolerance of thermolysin, in the following order: Cbz-Gly-Phe-NH2 < Cbz-Phe << phosphoramidon. The third compound exhibited stabilizing effects comparable with those of SMPI, which suggests that the interaction between SMPI and thermolysin was localized to the reactive site.

Catalytic activity of thermolysin under extremes of pressure and temperature: modulation by metal ions

The catalytic activity of thermolysin (TL), a Zn-dependent neutral protease from Bacillus thermoproteolyticus, has been studied over a wide interval of pressures (1 bar to 4 kbar) and temperatures (20 degreesC to 80 degreesC) by monitoring hydrolysis of a low-molecular-mass substrate, 3-(2-furylacryloyl)-glycyl-L-leucine amide. This reaction shows a very large negative value for the activation volume and, because of that, simultaneous increase in temperature and pressure leads to a significant (up to 40-fold) acceleration of the reaction. At pressures higher than 2-2.5 kbar, the reaction rate starts to decrease due to disactivation of TL. This disactivation is explained in part by pressure-promoted dissociation of zinc ion from the active site and can be inhibited by adding exogenous zinc. Thus, this thermostable protease does not specifically show a higher stability at high pressure in comparison with small mesophilic proteases.

The effect of high pressure on thermolysin

The effects of high pressure on thermolysin activity and spectroscopic properties were studied. Thermolysin showed distinct pressure-induced activation with a maximum observed at 200-250 MPa for a dipeptide amide substrate and at 100-120 MPa for a heptapeptide substrate. By examining the pressure dependence of the hydrolytic rate for the former substrate using a high pressure stopped-flow apparatus as a mixing device under elevated pressures, the activation volume of the reaction was -71 ml mol(-1) at 25 degrees C. Delta V++ was accompanied by a negative activation expansibility and a value of -95 ml mol(-1) was obtained at 45 degrees C. A prolonged incubation of thermolysin under high pressure, however, caused a time-dependent deactivation. These changes due to pressure were monitored by several spectroscopic methods. The fourth-derivative absorbance spectrum showed an irreversible change, mostly in the tyrosine and tryptophan regions, at a pressure higher than 300 MPa. Intrinsic fluorescence and circular dichroism measurements of thermolysin in solution also detected irreversible changes. All these measurements indicated that a change occurred at higher pressures and are explained by a simple two-state transition model accompanied by a large, negative change in the volume of reaction.

Structure of pressure-induced denatured state of human serum albumin: a comparison with the intermediate in urea-induced denaturation

The structure of human serum albumin (HSA) in the pressure-induced denatured state was investigated by fluorescence spectroscopy. HSA undergoes a conformational change in the pressure range from 0.1 MPa to 400 MPa, at 25 degrees C. Several ligands bind to specific sites in HSA, and the fluorescence spectra of these ligands were used to study the conformational state of this protein. The warfarin-binding site (site I) and the dansylsarcosine-binding site (site II), are located in subdomains II and III, respectively. The fluorescence spectra of these probes reflected the structural changes in each of these subdomains. Dansylsarcosine completely dissociated from its binding site in domain III above 300 MPa, but substantial affinity of warfarin remained in this pressure range. Similar results were obtained for the urea-induced denaturation of HSA; although dansylsarcosine completely dissociated at urea concentration above 6 M, warfarin remained bound to site I in domain II at these concentrations. These results suggest that the structure of domain III is unfolded both in the initial stages of both pressure- and urea-induced denaturation of HSA. HSA possesses a single tryptophan residue (Trp-214) in domain II, and fluorescence from this residue reflects structural changes in this domain. In the urea-induced denatured state of HSA, a red-shift in the wavelength of maximum fluorescence occurred over urea concentrations ranging from 4 M to 6 M. This shift indicated that a structural change in domain II occurred simultaneously with the unfolding of domain III in this concentration range. On other hand, the shift in the wavelength of maximum fluorescence of Trp-214 was comparatively small in the pressure range from 0.1 MPa to 400 MPa indicating that the environment of Trp-214 was not affected. These results indicate that preferential unfolding of domain III occurs in the pressure-induced denatured state of HSA.

Kinetic characterization of the neutral protease vimelysin from Vibrio sp. T1800

The kinetics of the hydrolysis of dipeptide and tripeptide substrates by the recently discovered neutral protease from Vibrio species T1800 (vimelysin) were studied. In the pH dependence of the apparent second-order rate constant, the pKa2 value of vimelysin (approximately 6.5) was significantly lower than thermolysin (8.3), although the pKa1 (approximately 5.1) values were comparable (5.0). The Kcat/Km(lim) parameter for hydrolysis of Fua-Gly-PheNH2 (Fua = furylacryloyl) was more than sevenfold greater than for Fua-Gly-LeuNH2. This higher specificity for Fua-Gly-PheNH2 was deduced for both Kcat and Km parameters. Fua-Phe-PheNH2 showed the highest Kcat/Km(app) value of the six substrates studied. The discrimination between Phe/Leu at the P1' site was most evident when the P1 site was not sufficiently filled. Reflecting the characteristically high proteolytic activity of vimelysin at lower temperatures [Oda, K., Okayama, K., Okutomi, K., Shimada, M., Sato, R. & Takahashi, S. (1996) Biosci. Biotech. Biochem. 60, 463-467], the Arrhenius plot of the apparent second-order rate constant for the hydrolysis of Fua-Gly-LeuNH2 showed an inverse temperature dependence; higher reaction rates were observed at lower temperatures. This was not merely due to the pKa shift nor to thermal denaturation of the enzyme coupling, but rather to the Kcat(app) parameter, which alone showed an inverse temperature dependence. A model containing two temperature-dependent forms of the active enzyme was postulated to explain this unique temperature dependence.

The pressure-induced structural change of bovine alpha-lactalbumin as studied by a fluorescence hydrophobic probe

The effect of pressure on bovine alpha-lactalbumin (LA) has been investigated by fluorescence methods. The intrinsic fluorescence spectra of holo-LA (CaII-bound LA) hardly changed in its intensity and maximum wavelength on increasing the pressure up to 400 MPa. In the intrinsic fluorescence spectrum of apo-LA (CaII-depleted form) the maximum wavelength was red-shifted, and the intensity was increased to a large extent by increasing pressure. The fluorescence titrations of both forms of LA were performed with a fluorescent hydrophobic probe 1,1'-bis(4-anilino)naphthalene-5,5'-disulfonate (bis-ANS) at various pressures, and binding constants (Kb) of bis-ANS were calculated. The Kb-value for holo-LA slightly decreased from 0.1 to 100 MPa and increased above 200 MPa. The Kb value for apo-LA gradually increased with increasing pressure up to 400 MPa. These results were explained by the difference in hydrophobic characteristics of holo- and apo-LA.

Modification of the single unpaired sulfhydryl group of beta-lactoglobulin under high pressure and the role of intermolecular S-S exchange in the pressure denaturation [single SH of beta-lactoglobulin and pressure denaturation]

Chemical modification reactions of the unpaired sulfhydryl group of beta-lactoglobulin (LG) under high pressure and the role of this group in the pressure-induced denaturation were investigated. When LG was incubated at 400 MPa (pH 6.8) for 1 h, dimerization through intermolecular reaction of SH was observed. The generation of the covalently linked dimers were prevented by the presence of N-ethylmaleimide (NEM), an agent for SH-specific modification. The reactivity of the SH group of LG, which is buried inside in its native state, was increased by high pressure, as a result of its exposure to the protein surface accompanied by the pressure denaturation. The effect of NEM was also observed in the fluorescence change caused by high pressure, in both the intrinsic fluorescence of LG and the retinol fluorescence of the LG-retinol complex. The control showed an irreversible change at neutral pH, but it became mostly reversible in the presence of NEM. Compatible results were obtained by CD spectroscopy. Inter- and intramolecular reactions of the SH group are suggested to be main causes for the pressure-induced irreversible denaturation of LG.

The pressure-dependence of two beta-glucosidases with respect to their thermostability

A comparative study of temperature and pressure effects were carried out by using two homologous enzymes exhibiting different thermostability and oligomery: almond beta-glucosidase and Sulfolobus solfataricus beta-glucosidase. Both the activity and stability were studied using an in-house built bioreactor allowing injection, stirring, sampling and on-line spectrophometric monitoring with retention of pressure up to 2.5 kbar and temperature control possible up to 150 degrees C. Almond beta-glucosidase, the most pressure sensitive enzyme of the two was continuously affected by pressure up to 1.5 kbar. Activation volume changes revealed that the inactivation of almond beta-glucosidase was due to both catalytic step inactivation and enzyme-substrate binding inactivation. Structural modifications generated by pressure, related to a loss of activity did not affect the global conformation of almond beta-glucosidase, after depressurization. In contrast, Sulfolobus solfataricus beta-glucosidase was a highly barostable enzyme. It maintained a half-life of 91 h at 60 degrees C and 2.5 kbar. Moreover, this enzyme appeared to be activated by pressure between atmospheric pressure and 2.5 kbar with a maximal activity at 1.25 kbar. However, this enzyme still displayed the best catalytic efficiency at atmospheric pressure because of a Km value drastically increased by pressure. Activation volume changes indicated that the hydrolysis reaction catalysed by Sulfolobus solfataricus beta-glucosidase, was alternatively favoured and disfavoured by pressure due to the catalytic step activation or inactivation associated with the enzyme-substrate binding step being continuously inactivated by pressure.

Hydrostatic pressure induces conformational and catalytic changes on two alcohol dehydrogenases but no oligomeric dissociation

A comparison between the pressure effects on the catalysis of Thermoanaerobium brockii alcohol dehydrogenase (TBADH: a thermostable tetrameric enzyme) and yeast alcohol dehydrogenase (YADH: a mesostable tetrameric enzyme) revealed a different behaviour. YADH activity is continuously inhibited by an increase of pressure, whereas YADH affinity seems less sensitive to pressure. TBADH activity is enhanced by pressure up to 100 MPa. TBADH affinity for alcoholic substrates increases if pressure increases, was TBADH affinity for NADP decreases when pressure increases. Hypothesis has been raised concerning the dissociation of oligomeric enzymes under high hydrostatic pressure ( < 200 MPa) [1]. But in the case of these two enzymes, unless the oligomers reassociate very quickly (< 1 min), the activity inhibition of YADH at all pressures and TBADH for pressures above 100 MPa is not correlated to subunit dissociation. Hence we suggest that enzymes under pressure encounter a molecular rearrangement which can either have a positive or a negative effect on activity. Finally, we have observed that the catalytic behaviour of alcohol dehydrogenases under pressure is connected to their thermostability.

Observation of the pre-steady state process in thermolysin catalysis with a fluorescent displacement probe at low pH

The pre-steady state process in the thermolysin-catalyzed hydrolysis of Cbz-Gly-Phe-Ala was observed at pH 4.5 by fluorescence stopped-flow method using Dns-Phe as a displacement probe. After the confirmation of the pre-equilibrium hypothesis for the binary interaction, the nonlinear substrate concentration dependence of the apparent kinetic constant for the pre-steady state process was analyzed and an existence of multi-intermediates was proposed.

Proteins under pressure. The influence of high hydrostatic pressure on structure, function and assembly of proteins and protein complexes

Oceans not only cover the major part of the earth's surface but also reach into depths exceeding the height of the Mt Everest. They are populated down to the deepest levels (approximately 11,800 m), which means that a significant proportion of the global biosphere is exposed to pressures of up to 120 MPa. Although this fact has been known for more than a century, the ecology of the 'abyss' is still in its infancy. Only recently, barophilic adaptation, i.e. the requirement of elevated pressure for viability, has been firmly established. In non-adapted organisms, increased pressure leads to morphological anomalies or growth inhibition, and ultimately to cell death. The detailed molecular mechanism of the underlying 'metabolic dislocation' is unresolved. Effects of pressure as a variable in microbiology, biochemistry and biotechnology allow the structure/function relationship of proteins conjugates to be analyzed. In this context, stabilization by cofactors or accessory proteins has been observed. High-pressure equipment available today allows the comprehensive characterization of the behaviour of proteins under pressure. Single-chain proteins undergo pressure-induced denaturation in the 100-MPa range, which, in the case of oligomeric proteins or protein assemblies, is preceded by dissociation at lower pressure. The effects may be ascribed to the positive reaction volumes connected with the formation of hydrophobic and ionic interactions. In addition, the possibility of conformational effects exerted by moderate, non-denaturing pressures, and related to the intrinsic compressibility of proteins, is discussed. Crystallization may serve as a model reaction of protein self-organization. Kinetic aspects of its pressure-induced inhibition can be described by a model based on the Oosawa theory of molecular association. Barosensitivity is known to be correlated with the pressure-induced inhibition of protein biosynthesis. Attempts to track down the ultimate cause in the dissociation of ribosomes have revealed remarkable stabilization of functional complexes under pseudo-physiological conditions, with the post-translational complex as the most pressure-sensitive species. Apart from the key issue of barosensitivity and barophilic adaptation, high-pressure biochemistry may provide means to develop new approaches to nonthermic industrial processes, especially in the field of food technology.

Effect of high pressure on EcoRI reactions

The effect of pressure on reactions of restriction endonucleases was investigated. No obvious irreversible (after) effect was observed for EcoRI, while a considerable irreversible inactivation was found for BamHI. Thus the EcoRI reactions against lambda DNA, pBR322 and pBluescript were studied under high pressure and little effect was observed on the overall reactions. The DNA concentration dependence of the kinetic data apparently fits the Michaelis-Menten type equation and the evaluated rate parameters were: Vmax = 6.2 +/- 0.24 and 7.0 +/- 0.22 (x 10(-2) nM/min) at 0.1 and 200 MPa, respectively; Km = 19 +/- 1.8 and 28 +/- 1.7 nM at 0.1 and 200 MPa, respectively. The apparent activation volume corresponding to kcat/Km was ca +1 mL/mol. A characteristic effect of pressure on the sequence specificity of these enzymes was seen in their star activity. Relaxed specificity was tightened by increasing pressure (200 MPa) with respect to that induced by low salt concentration or by the presence of organic solvent.

The catalytic activities of monomeric enzymes show complex pressure dependence

High hydrostatic pressures in the biologically relevant range (< or = 1,200 bar) are known to cause dissociation of oligomeric enzymes in vitro, whereas protein denaturation requires pressures far beyond this range. Pressure-induced inactivation phenomena attributable to neither of these effects are shown to occur in monomeric enzymes. Three different types of pressure dependence can be distinguished: (1) a linear dependence of catalytic rate constants on pressure, as predicted by the activated complex theory, observed for lysozyme and thermolysin; (2) a biphasic profile consisting of two linear contributions, found for trypsin; (3) maximum curves, as observed for both directions of the octopine dehydrogenase reaction. The third case may be ascribed to a pressure-induced decrease in the partial specific volume of the protein, resulting in reduced flexibility of the active site. This mechanism may also apply to the pressure-induced inactivation of assembly systems stabilized against dissociation in the cell.

A study on the inactivation of wheat carboxypeptidase. Implication of the transient active monomer and the half-site reactivity

The mechanism of inactivation of carboxypeptidase from wheat at high pH was studied kinetically and spectrophotometrically. Inactivation of wheat carboxypeptidase is characterized by initial, transient high activity, soon followed by loss of activity, accompanied by an increase in both fluorescence intensity and anisotropy and a decrease in circular dichroism. A scheme was proposed in which the enzyme undergoes dissociation into monomers, the total activity of which becomes twice that of the normal dimer on a mass basis, and soon further denatures and aggregates. Treatment of the enzyme with a bifunctional reagent partly prevented denaturation of the monomer and hence increased the peptide synthetic activity.

Engineering considerations for the application of extremophiles in biotechnology

Biotechnology may soon take greater advantage of extremophiles--microorganisms that grow in high salt or heavy metal concentrations, or at extremes of temperature, pressure, or pH. These organisms and their cellular components are attractive because they permit process operation over a wider range of conditions than their traditional counterparts. However, extremophiles also present a number of challenges for the development of bioprocesses, such as slow growth, low cell yield, and high shear sensitivity. Difficulties inherent in designing equipment suitable for extreme conditions are also encountered. This review describes both the advantages and disadvantages of extremophiles, as well as the specialized equipment required for their study and application in biotechnology.