Enzyme pressure effects

For the time being, our basic understanding of pressure effects is far from complete. However, some new developments concerning theory and application have occurred over the years. A short theoretical treatment of pressure effects was presented almost 30 years ago (Laidler, 1951). In this article we will present an extensive treatment of the present theoretical basis for pressure effects, incorporating contemporary knowledge of enzyme kinetics, physical biochemistry, and high-pressure theory. The theoretical level in this field is still not very sophisticated, but it is important enough so that theoretical considerations should be applied when future experiments are planned. 

The usual starting point in enzyme kinetics is the Michaelis-Menten equation for the reaction rate v. This also seems a convenient starting point for interpretation of pressure effects on enzyme mechanisms. It will be shown that this formalism may be deceptive if the definitions and interpretations have not been made clear from the beginning. For the mechanism... 

With the enzyme concentration fixed, it may be difficult to vary the substrate concentration to any large extent. Maybe only some limited range of substrate concentrations corresponds to linear rate curves. Sometimes the best combination is high substrate concentration and low enzyme concentration. But high substrate concentrations may have side-effects, e.g., inhibition. If this is so, the pressure effect will probably be very concentration-dependent. 

Pressure may cause several changes in enzymes, as well as some changes which are not directly associated with the catalytic process. These changes may include conformational changes and subunit dissociation-association processes. Pressures above 4000 bar may induce conformational changes to such an extent that the enzyme in effect becomes irreversibly denatured. These are dealt with in the next section. In this section we will deal with lower pressures and reversible processes, namely, interactions between subunits in quaternary structures. For most multimeric enzymes, the maintenance of... 

Many of the investigations are carried out at low temperatures and/or at pH values deviating somewhat from neutrality. It has earlier been emphasized that the influence from factors such as temperature, pressure, pH, concentrations, ionic strength, and salt effects must be considered when pressure effects are discussed. This is because conditions that are optimal to one enzyme may be intolerable to another. After all, we are dealing with enzymes from microorganisms, cold-blooded, and warm-blooded animals. Such complications make comparison of pressure effects on enzymes nearly meaningless. 

Perhaps it would be most informative to study the enzymes at their respective physiological conditions, at least for the purpose of predicting the effect of pressure on a living organism. Nevertheless, deliberate changes of conditions may be valuable when pressure is used to probe structure and mechanism. As we learn to understand the role of protein structure in the determination of pressure effects, we may be able to predict the effects on one enzyme from knowledge of the effect on another. Then, we may be able to gain information about pressure effects on human enzymes. 

The Theory of Pressure Effects of Enzymes Eddie Morild... 

High pressure has proven to be a useful tool in biochemistry for the study of a number of cell-mediated processes, the most important being the effect on gene expression. The pressure effect on the stability of enzymes and biopolymers is a topic of general interest that may generate a number of possible applications in the area of food science. Biochemistry and biophysics continue to attract many new research groups, especially in the field of protein chemistry. Pressure may be a tool to obtain unique textures and provide biochemical products with new properties. 

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