What is the likely reason that enzyme activity is so low at 60c?

Answer 1

At temperatures after the optimum for the enzyme , the enzymes become denatured. This is because the active site of the enzyme becomes distorted , meaning no substrates can bind with the site in anabolic/catabolic reactions. The polypeptides that make up these enzymes unravel , which changes the quaternary structure , causing this distortion of the active site. I hope this is what you're looking for , ORCA-93 :)

Answer 2

@ 60 °C ? ...well, enzymes are proteins, and proteins mostly get denaturated at such great heat...so they become nonfunctional.

There is however an enzyme called 'Taq polymerase' from a bacteria called 'Thermus Acquaticus' that can whitstand such high temperatures (that is because this bacteria lives in hot waters).