Oxidoreductase involved in the biosynthesis of cannabinoids-related terpenophenolic natural products, which have pharmacological activity (Ref.5, Ref.3, PubMed:9862135). Catalyzes the oxidative cyclization of the monoterpene moiety in cannabigerolic acid (CBGA) producing cannabichromenic acid (CBCA), which exhibits anti-inflammatory, antifungal and antimicrobial effects (Ref.5, Ref.3, PubMed:9862135). Can also use cannabinerolic acid (CBNRA) as substrate (PubMed:9862135). Unable to catalyze the production of delta(9)-tetrahydrocannabinolate (THCA), the precursor of Delta(1)-tetrahydrocannabinol (PubMed:16143478). A + cannabigerolate = AH2 + cannabichromenate A + cannabinerolate = AH2 + cannabichromenate Binds 1 FAD per subunit in a bicovalent manner. Inhibited by hydrogen peroxide H(2)O(2) and FMN (PubMed:9862135). Completely repressed activity by Hg(2+) (PubMed:9862135). kcat is 0.04 sec(-1) with cannabigerolic acid as substrate. Optimum pH is 6.5. Secondary metabolite biosynthesis; terpenoid biosynthesis. Monomer (By similarity). May form homodimer (PubMed:9862135). Expressed in young leaves. The FAD cofactor is bound via a bicovalent 6-S-cysteinyl, 8alpha-N1-histidyl FAD linkage. Several isoforms of the inactive tetrahydrocannabinolic acid synthase found in the 'fiber-type' cannabis plants exist due to polymorphism. Belongs to the oxygen-dependent FAD-linked oxidoreductase family.