what is function of protease?

[no idea]

what is function of protease? IF it digests protein, then will it digest enzyme as enzymes are made of protein?

[aychamo]

Proteases (ex: pepsin, trypsin, chymotrypsin) are a group of enzymes that break down (hydrolyze) peptide bonds of proteins.

As for why they don't digest each other, they probably don't have an affinity for each other.

[Ethanol]

Enzymes are highly specific in nature. There is a theory that states that the substrate interlocks into the enzyme just as a key fits into a lock to produce a transition state finaly forming the products. A specific enzyme interlocks with only specific subtrate to give a transition state.