The velocity of most chemical reactions increases exponentially with temperature. The data conform with considerable accuracy to the Arrhenins equation which is written conveniently in the form
where k, and k, are the rates of reaction at the absolute temperatures TI and T,, R is the gas constant, and p is the temperature characteristic representing the activation energy in calories of the reaction (Glasstone, '33). Although at first only a n empirical relationship, this equation has since been amply confirmed from theoretical physics and chemistry (Crozier and Hoagland, '34). The temperature characteristic, or p value, is considered to represent the energy in calories required to activate 1 gm. mol of the catalyst for the reaction. If this is true, different reactions having the same catalyst will have the same temperature characteristic. This has been experimentally verified for certain inorganic catalysts.
The same postulates for the influence of temperature on reaction velocity would be expected to apply to biochemical reactions catalyzed by enzymes. The p value, or critical increment, for such a reaction should be constant over the whole range of temperature until the inactivation temperatnre of the enzyme is reached. The absolute velocity of the reaction will be altered of course, when certain properties of 61 62 IRWIN W. SIZER the medium are changed, for example the (H+) of the solution, the electrolyte concentration, and the relative amounts of substrate and enzyme. The temperature characteristic should be independent of such environmental changes, however, unless these alterations have modified the physical and chemical structure of the enzyme. If p characterizes the catalyst, and not the reaction, then the same temperature characteristic should be obtained when a single enzyme acts on different substrates. Conversely, enzymes which are chemically distinct should yield different p values when acting on the same substrate.
Previous workers have found that the tcmperature characteristic for most enzyme reactions is not a constant, but decreases with rise in temperature. F o r yeast invertase ~1 was found to decrease linearly with temperature according t o the equation proposed by Vosburgh (Nelson and Bloomfield, '24) : p = 12,300 -117t. Nelson and Bloomfield, using the temperatures 25, 30 and 35"C., found that p decreased rapidly with rise in (H+) and temperature, but was relatively constant in the region of pH for optimum activity ( p H 4.7). Auden and Dawson ( '31) using concentrated sugar solutions and high temperatures also reported a decline of p with temperature. Kertesz ('33) found that p declined not only at temperatures above 0ยฐC. but at temperatures below this point as well.
The above results are all contrary to what would be expected on theoretical grounds. According to some (Raldane, '30) this fact throws doubt on all calculations of critical increments f o r biological processes, since a biological system is assumed to be more complex than a simple enzyme reaction. Because of the discrepancy between expe1:imental results and theory, this study of catalyzed cane sugar hydrolysis as a function of temperature was undertaken. METHOD Sugar solutions were placed in a 200-mm. polariscope tube and the course of the reaction followed by means of a Schmidt and Haensch polarimeter. -9 Mazda 60-watt blue bulb was used throughout as the source of illumination. The tempera-