EFFECTS OF PKESSURE 849 



— 10 ml/mole for the formation of the enzyme-urethane complex) but at 

 50° this reverses to a vokmie increase, which becomes quite large around 

 60-65°. Of course, at the higher temperatures one might expect the situa- 

 tion to become more complex because of the instability of the enzyme 

 and the multiple reactions that may be simultaneously proceeding. In the 

 normal temperature range, high pressure increased the inhibition and the 

 volume slightly decreased as mentioned above. What might be the expla- 

 nation for this effect? The volume change is equivalent to that seen with the 

 appearance of one ionic charge so it is possible that the binding of the 

 urethane to the enzyme brings about an ionization of an enzyme or an inhi- 

 bitor group, or creates a strong clipole. The pressure effect might also be 

 on an enzyme acidic group to promote ionization and increase the sensi- 

 tivity of the enzyme to the urethane. However, /?-fructofuranosidase has 

 pica's at 2.6-3.0 and 6.6-6.8, and the experiments w^ere run at pH 4.5, so 

 that it is unlikely that such a mechanism is correct. If the urethane fa- 

 vored the denaturation of the enzyme, or shifted the equilibrium in favor 

 of a denatured form, one would exi:)ect an increase in volume (which is 

 what might occur at higher temperatures). A change in the configuration 

 of the active site due to hydrogen bonding between urethane and the poly- 

 peptide chains is a remote possibility. Whatever explanation is correct, 

 this example serves to illustrate the inherent complexity of such studies 

 and issues a warning against the facile interpretation of the results. 



Effects of Pressure on Inhibitions in Cellular Systems 



Many studies have shown the marked effects pressure may have on cell 

 motility — for example, muscle contraction, ciliary beating, and cell cleav- 

 age — and these effects have been successfully interpreted in terms of 

 changes in the protoplasmic viscosity or shifts in the sol-gel state. Such 

 physical alterations must be important in the responses of some metabolic 

 systems to high pressure but nothing is known about this as yet. It would 

 be most interesting to know what the effects of high pressure are on the 

 tricarboxylic acid cycle in isolated mitochondria. In multienzyme systems, 

 the effects of pressure must indeed be quite complex because each step will 

 be affected to some extent. The only cellular metabolic system studied quan- 

 titatively with respect to pressure is the luminescence of certain bacteria 

 by Johnson and his colleagues. These experiments were usually considered 

 to represent the effects on the luciferase reaction but there are other en- 

 zymes that are probably involved in determining the intensity of the lu- 

 minescence, so that it may be safer to envision a multienzyme system. 

 Indeed, it is likely that in bacteria there is no enzyme functioning like lu- 

 ciferase in fireflies. Evidence against the single-enzyme interpretation was 

 present in the early work. For example, the luminescence of different spe- 

 cies of bacteria is affected differently by an increase in the pressure: the 



