ARS | Publication request: Presence of epoxide hydrolase activity in Aspergillus niger: Hydrolysis of 6', 7'-epoxybergamottin to 6', 7'-dihydroxybergamottin

Submitted to: Subtropical Technology Conference Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: September 15, 2007
Publication Date: October 18, 2007
Citation: Myung, K., Manthey, J.A., Narciso, J.A. 2007. Presence of epoxide hydrolase activity in Aspergillus niger: Hydrolysis of 6', 7'-epoxybergamottin to 6', 7'-dihydroxybergamottin. Subtropical Technology Conference Proceedings. 58:16.

Technical Abstract: The 6', 7'-epoxybergamottin (EB) is one of major furanocoumarins in grapefruit. Previously, we have shown that Aspergillus niger has a capability of metabolizing EB into 6', 7'-dihydroxybergamottin (DHB), which is further metabolized to bergaptol and bergaptol-5-sulfate in vivo. In this study, we attempted the biotransformation of EB into DHB in vitro. When EB was incubated with enzyme extract prepared from 4-day A. niger culture, an epoxide hydrolase activity was detected where EB was hydrolyzed into DHB within 30 min at pH 8.0. The EB incubated with boiled enzyme extract was not hydrolyzed into DHB, demonstrating that the epoxide hydrolase activity is present in the fungus. Specific activity of epoxide hydrolase was approximately 28.2 nmole/hr/mg protein. Similar hydrolytic activity was obtained from enzyme extracts prepared from either A. niger culture with or without pre-treated EB, indicating that the hydrolytic activity is not induced by EB, rather the epoxide hydrolase activity is constitutively present. Since the hydrolytic reaction occurred in our assay system only containing a buffer, EB, and crude extract, the hydrolysis of EB by epoxide hydrolase would be accomplished in a cofactor-independent manner. Overall, our data support that the epoxide hydrolase activity is present in A. niger, in which EB is hydrolyzed into DHB.