The effect of pressure on the activity of ribonuclease

The interactions of nucleic acids at elevated hydrostatic pressure

The application of elevated hydrostatic pressure on the order of a few thousand bar provides insight into the molecular forces responsible for stabilizing the conformations and non-covalent interactions of biological molecules in aqueous solution. In particular, the parameters derived from these studies have enabled researchers to glean information regarding the importance of hydration in the energetics and kinetics of these systems. This review presents data concerned with the application of hydrostatic pressure to study the thermodynamics, kinetics, and structure of nucleic acids and the interactions between nucleic acids and proteins, enzymes, and drugs. These complexes often form extremely stable non-covalent complexes in which electrostatic interactions play an important role. The sensitivity of these interactions to pressure offers a valuable experimental tool for investigating the energetics of the complexes.

Partially folded states of the capsid protein of cowpea severe mosaic virus in the disassembly pathway

The different partially folded states of the capsid protein that appear in the disassembly pathway of cowpea severe mosaic virus (CPSMV) were investigated by examining the effects of hydrostatic pressure, sub-zero temperatures and urea. The conformational states of the coat protein were analyzed by their intrinsic fluorescence, binding of bis(8-anilinonaphthalene-1-sulfonate) (bis-ANS) and susceptibility to trypsin digestion. CPSMV could be disassembled by pressure at 2.5 kbar. Intrinsic fluorescence and hydrodynamic measurements showed that pressure-induced dissociation was completely reversible. Virus pressurization in the presence of ribonuclease revealed that viral RNA was not exposed, since it was not digested by the enzyme, suggesting the maintenance of protein-nucleic acid interactions under pressure. When the temperature was decreased to -10 degrees C under pressure, CPSMV disassembly became an irreversible process and in this condition, viral RNA was completely digested by ribonuclease. These results suggest a relationship between protein-RNA interactions and CPSMV assembly. Bis-ANS binding and trypsin digestion of coat proteins revealed that they assume a different conformation when they are denatured by low temperatures under pressure or than when they are denatured by urea at atmospheric pressure. The results indicate that the coat proteins can exist in at least four states: (1) The native conformation in the virus capsid; (2) bound to RNA when the virus is dissociated by pressure at room temperature, assuming a conformation that retains the information for reassembly; (3) free subunits in a molten-globule conformation when the virus is dissociated by low temperature under pressure; and (4) free subunits completely unfolded by high concentrations of urea.

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.

Pressure dependence of thermolysin catalysis

A comparison of the pressure and temperature dependences of the catalytic reaction of thermolysin, a thermostable neutral protease from Bacillus thermoproteolyticus, with those of a non-thermostable neutral protease from Bacillus subtilis revealed a distinct difference in Km values of these enzymes for 3-(2-furyl)acrylyl-blocked dipeptide and tripeptide substrates, but not for Kcat. Namely, the volume changes for the binding process (delta V) for these substrates and several competitive inhibitors were -20- -30 ml/mol for thermolysin and nearly 0 ml/mol for the non-thermostable neutral protease. The enthalpy and entropy changes for the binding process were negative for thermolysin, but positive for the latter enzyme. The activation volumes (delta V not equal to) for the kcat process were 25 -35 ml/mol for both proteases, and activation enthalpy and entropy showed no significant difference between the two enzymes. The characteristic difference in the pressure and the temperature dependences seen for the binding process is discussed in relation to the thermostability of the proteases.

High pressure enzyme kinetics of dextransucrase

The pressure dependence of enzymatic dextran formation has been observed up to 1000 at for several substrate concentrations. First order denaturation effects could be separated from the thermodynamic effects, which lead to a volume of 30.4 to 44.0 ccm per mole for the formation and -13.6ccm per mole for the activation of the enzyme-substrate complex. Denaturation depends on the substrate concentration. This leads to the conslusion that only the free enzyme is denatured, wheras the ES complex is stable.