At what temperature is active yeast killed?

Answerbelow 50 F is too low, and above 140 F is too high. 80 to 90 F is perfect

*Yeast cannot die below 50 F. If that where true then we would not be able to freeze unbaked bread dough and that is something I do on a regular basis therefore the low temp must be lower than freezing.
around 70 celcius, when its enzymes start denaturing