Ribokinase is enzyme participating in ribose and deoxyribose phosphate metabolism. It is used to produce nucleosides with modified ribose residue.

In enzymology, a protocatechuate 3,4-dioxygenase (EC 1.13.11.3) is an enzyme that catalyzes the chemical reaction:3,4-dihydroxybenzoate + O2? 3-carboxy-cis,cis-muconate.

This enzyme belongs to the family of oxidoreductases, specifically those acting on the aldehyde or oxo group of donor with NAD+ or NADP+ as acceptor.