Protease endonuclease acts on peptide bonds that are joined within protein molecules and cuts them off to form proteins, oligopeptides and amino acids with small molecular weight. According to the optimal pH value of the reaction, it is divided into acid protease enzyme
, neutral protease and alkaline protease
. Protein exonuclease hydrolyzes the peptide bonds one by one from the end of the free amino or carboxyl groups of protein molecules or polypeptides to form free amino acids, such as aspergillus oryzae and aminopeptidase.