structure known is that of the gas vesicle.Gas vesicle membranes can collapse at pressures as low as 0.06 MPa (equal to 6 meters depth). Elevated pressure also has commercial applications.High pressures [hundreds of megapascals,1 megapascal (MPa)9.9 atmospheres 10 bar]can be used in place of temperature for food pasteurization,in which case there is less of an effect on food color or flavor.High pressure is also used for food processing, where it can be used to form gels,promote protein coagulation,or lipid phase transitions.Also,because pressure influences enzyme reactions in ways that are very different from osmotic pressure or temperature effects,there is interest in obtaining piezophilic derivatives of yeast and antibiotic producing bacteria to alter fermentation products for food and natural product formation, respectively. During the normal activity of humans there are tissues,particularly the cartilage of our joints,which routinely experience considerable hydrostatic pressure. Indeed these pressures or loads on our joints are important for human health (this is one of the reasons astronauts experiencing weightlessness for prolonged periods can suffer health problems).Simply standing can result in 20 MPa pressure in the human hip.Even we terrestrial mammals are all piezophiles to some extent! A.Pressure effects are related to volume changes Pressure changes will affect any biological process that occurs with a change in system volume.Intuitively this should be clear.For example,if a volume expansion must accompany a process,e.g.,adding gas to a fish's swim bladder to increase theorgan's volume,this process will be more difficult under higher pressure.Conversely,if a decrease in volume accompanies a process,then elevated pressure will favor the process. These intuitively obvious relationships can be expressed mathematically as follows: 1)KK exp(-PAV/RT)and 2)k =k exp(-PAV /RT) These two equations express the relationship of either the equilibrium constant (K)or rate constant (k)of a reaction to pressure,as determined by the size of the volume change that takes place during either the establishment of equilibrium (AV)or the formation of the activated complex (AV).K and k are the equilibrium and rate constants,respectively, at 1 atmosphere (atm)pressure;K and k are the constants at a higher pressure, p.R is the gas constant and T is absolute temperature.Equilibrium constants,unlike rate constants,are also dependent on the concentration of substrates and products. For example,proteins whose polymerization are sensitive to high pressure at one 33 structure known is that of the gas vesicle. Gas vesicle membranes can collapse at pressures as low as 0.06 MPa (equal to 6 meters depth). Elevated pressure also has commercial applications. High pressures [hundreds of megapascals, 1 megapascal (MPa) ≈ 9.9 atmospheres = 10 bar] can be used in place of temperature for food pasteurization, in which case there is less of an effect on food color or flavor. High pressure is also used for food processing, where it can be used to form gels, promote protein coagulation, or lipid phase transitions. Also, because pressure influences enzyme reactions in ways that are very different from osmotic pressure or temperature effects, there is interest in obtaining piezophilic derivatives of yeast and antibiotic producing bacteria to alter fermentation products for food and natural product formation, respectively. During the normal activity of humans there are tissues, particularly the cartilage of our joints, which routinely experience considerable hydrostatic pressure. Indeed these pressures or loads on our joints are important for human health (this is one of the reasons astronauts experiencing weightlessness for prolonged periods can suffer health problems). Simply standing can result in 20 MPa pressure in the human hip. Even we terrestrial mammals are all piezophiles to some extent! A. Pressure effects are related to volume changes Pressure changes will affect any biological process that occurs with a change in system volume. Intuitively this should be clear. For example, if a volume expansion must accompany a process, e.g., adding gas to a fish's swim bladder to increase theorgan's volume, this process will be more difficult under higher pressure. Conversely, if a decrease in volume accompanies a process, then elevated pressure will favor the process. These intuitively obvious relationships can be expressed mathematically as follows: 1) K p = K 1 exp(-P∆V/RT) and 2) k p = k 1 exp(-P∆V † /RT) These two equations express the relationship of either the equilibrium constant (K) or rate constant (k) of a reaction to pressure, as determined by the size of the volume change that takes place during either the establishment of equilibrium (∆V) or the formation of the activated complex (∆V † ). K 1 and k 1 are the equilibrium and rate constants, respectively, at 1 atmosphere (atm) pressure; K p and k p are the constants at a higher pressure, p. R is the gas constant and T is absolute temperature. Equilibrium constants, unlike rate constants, are also dependent on the concentration of substrates and products. For example, proteins whose polymerization are sensitive to high pressure at one