How do enzymes soften meat?

SInce meat is made of protein, an enzyme which can digest protein called protease can soften the meat by digesting some of the meat.
原理:
The enzyme bind to the active site of the substrate(protein molecules), forming an enzyme-substrate complex. After some time for the reaction to take place, protein would be digested in amino acids.This enzyme action of breaking down a substance is called catabolic reaction while the opposite action is called anabolism.

肉在young animal是比老soft很多的 , 當muscle getting old the meat become quite tough .這是因為the tissue 連接muscle 有很多根及脂肪等 , 將tissue拉緊that the muscle can have better power but it is hard to eat it . 所以要很久才林 , 或用刀背擊muscle , 用針刺肉或用soda葉等方法 . 而用enzymes such用木瓜汁 , pineapple or Kiwi fruit. 一肉因此三種生果有大量digestive enzymes which can digest some of connective tissue biding the muscle together , 根及脂肪 . 所以在未前葉10-15minutes 能tenderize the meat .一經加熱enzymes are functionless .

the samefor you, especially if you give them ideal conditions. ... In the US, meat tenderiser may be worth trying as a source of protease.