8.2.2 Cannabidiolic Acid Synthase
8.2.2.1 Biochemical Properties
CBDA is the dominant constituent of thefiber-typeC. sativa(also known as hemp).
In contrast to the drug-type plants (Shoyama et al. 1975 ), thefiber-type produces a
large amount of CBDA, but only small amount of THCA. Using afiber-type
(CBDA strain), we have identified a novel enzyme termed CBDA synthase that
catalyzes oxidative cyclization of CBGA to form CBDA (Taura et al. 1996 ).
The gene encoding CBDA synthase was cloned using a similar strategy as was
implemented previously for THCA synthase (Taura et al.2007b). Degenerate PCR
and rapid amplification of the cDNA ends identified a gene consisting of a 1632
nucleotide open reading frame, encoding a 544-amino acid polypeptide containing
a 28-amino acid signal peptide. The deduced primary structure had a very high level
(*84%) of identity with THCA synthase (Sirikantaramas et al. 2004 ), and a 40–
50% sequence identity with VAOflavoprotein family members such as the ber-
berine bridge enzyme (Dittrich and Kutchan 1991 ). In addition, the deduced amino
acid sequence of CBDA synthase revealed that there were conserved His and Cys
residues responsible for bi-covalentflavinylation as described for THCA synthase
(Shoyama et al. 2012 ).
The insect cell-derived recombinant enzyme exhibited spectroscopic properties
characteristic to covalentlyflavinylated proteins. Biochemical characterization of
the recombinant enzyme demonstrated that CBDA synthase catalyzes the stereos-
elective oxidocyclization of CBGA in a FAD dependent manner (Fig.8.7).
Apparently, the reaction mechanism catalyzed by CBDA synthase is similar to that
of THCA synthase. In both instances, FAD temporally accepts the electrons from
the substrate, and then FAD is re-oxidized using molecular oxygen. On the other
hand, the important difference between these two reactions is seen in the proton
Fig. 8.7 The reactions catalyzed by cannabidiolic acid (CBDA) synthase and tetrahydrocannabi-
nolic acid (THCA) synthase. The catalytic base for CBDA synthase is unknown. CBGA
cannabigerolic acid
8 Cannabinoids: Biosynthesis and Biotechnological Applications 191