The optimal temperature of enzymes in humans is about 37c, the same as the human body's temperature. However, some enzymes work at higher temperatures than 37 but not very high because higher temperatures denatures (destroy) the enzymes.
Some enzyme function only in specific conditions, they are activated only in suitable environment. some work only in neutral environment. all ptyalin in saliva works only in the mouth which has a pH...
It is very specific to the enzyme. Enzymes living inside cells have completely different conditions to those living outside the cells. That's why our body has the E.R(Endoplasmic Reticulum). It uses...
I believe it's 7.3, the pH of human blood, as most enzymatic reactions occur there. However, there are special enzymes, such as the ones which are in the stomach, which work best at around a pH of 2.