#Science for Innovation

Temperature dependence of enzymes and organisms

The concentrations of greenhouse gases (CO2, CH4, N2O) in the atmosphere are critically dependent on ecosystem processes. The response of organisms and ecosystems to changes in temperature are very complex. However, we need to understand the principles that underpin the temperature dependence of organism and ecosystems in order to predict how they will respond to changing temperature.

The research group of Professor Vic Arcus has published a seminal new paper in biochemistry: The Inflection Point Hypothesis: The Relationship between the Temperature Dependence of Enzyme-Catalyzed Reaction Rates and Microbial Growth Rates.

Enzymes are extraordinary catalysts that enable life to occupy nearly every available niche on our planet. These large, yet delicate, molecules show unusual responses to changes in temperature and this has a significant impact on how biological systems respond to temperature. Enzymes generally have an optimal temperature for their activity. If one exceeds this temperature, then enzyme activity drops away quickly. An intriguing and well known observation is that the optimal temperature for enzyme activity is generally significantly higher than the optimal growth temperature for the growth of the parent organism.

For example, the optimal temperature for glucokinase (an E. coli enzyme) is 46 °C whereas the optimal growth temperature for E. coli growth is 37 °C. Hence, the question arises - “what is the relationship between the temperature dependence of E. coli enzymes and the temperature dependence of E. coli growth?”. Our paper proposes “the inflection point hypothesis” which suggests that the inflection point on the temperature-rate graph for enzymes dictates where the optimum growth temperature for the organism will sit. This point is the steepest point on the temperature-rate curve for individual enzymes which is advantageous for the organism. It is also the point where all the enzyme rates are well coordinated should the temperature change. Hence, evolution will work towards placing the inflection points for individual enzymes at the environmental temperature for the organism. When temperatures go above the inflection points for individual enzymes, there is a catastrophe because enzyme rates diverge and hence the organism fails quickly at higher temperatures.

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