CATALYSIS: THE GUIDE OF LIFE 105 



reaction may be either endothermic or exothermic), is generally used 

 to preheat reactants, to help initiate other processes, or to raise steam 

 for general uses. 



Temperature Control in Biocatalysis 



Most living things die on exposure for varying times to the 

 temperature of boiling water, especially in the presence of mois- 

 ture. Some dry spores are more resistant. E. Zettnow reported 14 

 that some organisms in lime paste from a sugar factory survived 

 heating for 30 minutes at 310-320° C. Subsequent tests reduced 

 the killing temperature to 199° C and 220° C. In nature only 

 those biological systems and structures survive which keep temper- 

 atures down to non-lethal levels, by protecting the delicate, heat- 

 susceptible catalysts upon which life depends, against too high and 

 too localized a liberation of heat. How is this accomplished in 

 the cell? 



Three main factors seem to be at work. (1) The over-all reac- 

 tion is broken down into a series of successive chemical steps, 

 mediated by different catalysts or catalyst areas, so that the whole 

 reaction proceeds in what may be called a step-wise manner. 

 (2) The intermediate products must move from one catalyst area 

 to another (which takes time), and the total heat of the reaction 

 is gradually set free at distributed areas in what may be called a 

 spot-wise manner. (3) The biocatalysts are surrounded by aque- 

 ous cytoplasm; and water, with its high specific heat, helps to 

 absorb and distribute the heat energy liberated. 



The net result is that biological reactions usually proceed at a 

 very gradual rate, without sudden and violent local temperature 

 increase; this would be fatal, although the normal body temper- 

 ature is maintained by the regulated liberation of heat. Many 

 other factors are operative in control of body temperature, apart 

 from orderly liberation of heat by the biocatalysts specific to the 

 particular kind of animal. In cold-blooded animals (poikilo- 

 therms), the body temperature is much influenced by that of the 

 surroundings. Migration or descent underground protects some 

 against freezing to death, while others seek shade to prevent death 

 from too long an exposure to the sun (e.g., rattlesnakes). The 

 temperature of warm-blooded animals (home other ms) tends to re- 

 main constant, despite variations in the temperature of their 

 surroundings; but it varies greatly with the position of the animal 

 in the taxonomic scale. 15 



