Re: how does renaturation affect a curve showing denaturation?

[Moderator's note: This answer is a follow up to an earlier answer of Rafael's regarding the denaturation of pectinase (1142467237.Bc).]

1) Renaturation:
Sometimes you can change something in an enzyme's environment such as pH, and the enzyme will denature, and then when you change the environment back the process reverses itself and the enzyme 'renatures'. However, when enzymes are denatured with heat, the process is usually irreversible. So, in the case of your experiment heating pectinase, I don't think that renaturation is a factor.

2) Exponential decay curve:
I don't think I can explain the fundamental reasons why an exponential decay curve describes thermal denaturation of an enzyme; it is connected to the 'kinetics' of this process (any basic chemistry textbook can explain a little about chemical reaction kinetics; enzyme denaturation is not a chemical reaction, but same ideas of kinetics apply). But the important feature of the denaturation curve is that it shows that the 'half-life' of an active enzyme is pretty much constant at a given temperature -- if your enzyme has a half life of 2 minutes at 70C and you have 100% activity at time 0, then you will have 50% activity at 2 minutes, 25% activity at 4 minutes, and so on. Try plotting out a series like this look at the shape of the graph. Is it linear? (Plot at least 10 points).

*Please note: The author is answering on his own behalf, and his answer does not represent a statement from the USDA.