Biology question please help!!?

An enzyme needs optimal temperature and pH conditions. Too hot, the proteins in the enzyme denature and cease to function. Too cold, I believe there's something to do with the lowered speed of molecular activity. The substrates would be moving too slowly to attach to the enzyme? Too acidic (salting or pickling) or basic, it's outside of the enzyme's optimal range, I can't remember why specifically. Hope I helped a little bit at least.