I have to do a research about the enzymes in the human body and the things that affect them. I know that the body temperature affects the activity of enzyemes but I'd like to know if the outer temperature of the air affects them, too? When the temperature goes to 47°C or more we get tired and exhausted. Is this because the activity of enzymes decrease or is something else?!

  • $\begingroup$ Is this a homework question? What are your ideas for solving the question? $\endgroup$ – Chris Oct 20 '14 at 18:48
  • $\begingroup$ @Chris no i do a research and this's a part on it but i can't find the answer $\endgroup$ – Rehab Tarek Oct 20 '14 at 18:50

Enzymes usualy have a relative narrow temperature optimum, for those of our body this is usually around 37°C. It is around 37,2°C in the morning and goes slightly up to 37,7°C in the evening (see reference 1 for details). The temparature optimum for most enzymes looks somewhat like displayed in the figure (from here, interesting to read):

enter image description here

Enzymes are relatively tolerant to lower temperatures (although their reaction rate is much lower), but generally they work. If you go too high with the temperature, the activity will soon be reduced to zero, as the enzymes are denaturated and are not able to catalyze any reaction.

The human body does quite a lot to control its temperature and to keep it within a pretty small limit. It does either excessive sweating (when it's hot) or shivering (when it's cold) to maintain its temperature within or at least near the optimum. For further details on the themorgulation have a look on the Wikipedia article on this topic or reference 2 and 3.

Although our enzymes work at slightly lower reaction rates when the body temperature is higher (think of fever), this is not a major issue. Slightly higher temperatures can thus be tolerated, although you don't feel very nice.

The effect of to hot temperatures is different, though. It is mostly due to not consuming enough water, so that the body has not the possibility to control its temperature via sweating. This condition will ultmatively lead to a heatstroke, see here for more details. Before you reach the temperature in which your enzymes reaction rate will go down drastically, you have long collapsed.


  1. A critical appraisal of 98.6 degrees F, the upper limit of the normal body temperature, and other legacies of Carl Reinhold August Wunderlich.
  2. Skin blood flow in adult human thermoregulation: how it works, when it does not, and why.
  3. Thermoregulation: some concepts have changed. Functional architecture of the thermoregulatory system
  • $\begingroup$ "Although our enzymes work at slightly lower reaction rates when the body temperature is higher (think of fever)..." I'm very puzzled by this statement. Do you have support for it? Without reading, I would posit that the body is metabolizing more quickly, thus generating additional heat. $\endgroup$ – anongoodnurse Oct 21 '14 at 3:48
  • $\begingroup$ He is doing more metabolism, not necessarily faster. $\endgroup$ – Chris Oct 21 '14 at 11:57
  • $\begingroup$ Sorry to repeat the request, but do you have support for that? $\endgroup$ – anongoodnurse Oct 21 '14 at 12:52
  • $\begingroup$ @anongoodnurse Have a look at this and this articles. They both show the activity of enzymes depending on the temperature. And both show a sharp decline in activity above 37°C. The first is acid phosphatase, the second pancreatic lipase. $\endgroup$ – Chris Oct 21 '14 at 20:02
  • $\begingroup$ Good grief! The first reference is about two enzymes, one from Pseudomonas and one from wheat! Since neither of these organisms are thermoregulatory, they do not even apply to warm blooded animals. $\endgroup$ – anongoodnurse Oct 22 '14 at 1:47

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