|A fact from Enzyme appeared on Wikipedia's Main Page in the Did you know? column on 13 May 2010.|
I'm not too sure about saying 'enzymes are like eggs'. I'm fairly sure I've read somewhere that you can make a boiled egg liquid again, and similarly, heat denaturing an enzyme does not necessarily permanently change it. Depending on the enzyme, lowering the temperature might restore its activity, or even using some kind of in vitro refolding system may be able to bring it back from a denatured state. I know that the whole point of this page is that it's supposed to be simple, but regardless of target audience, I don't think you should go using absolutes if they're not strictly true.
Also, enzymes work at multiple temperatures and pH's. However, the optimal efficiency for the reaction depends on the temperature and pH, and usually occurs at one specific set of conditions. Gosh golly.
In most cases, the optimum pH is 7. Places like the stomach will of course have different pH's because of the hydrochloric acid down there.