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Journal of Biochemistry Advance Access published online on October 9, 2009
Journal of Biochemistry, doi:10.1093/jb/mvp155
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© The authors 2009. Published by Oxford University Press on behalf of the Japanese Biochemical Society. All rights reserved.

Atypical kinetics of cytochromes P450 catalyzing 3'-hydroxylation of flavone from the white-rot fungus Phanerochaete chrysosporium

Noriyuki Kasai1, Shinichi Ikushiro1, Shinji Hirosue2, Akira Arisawa2, Hirofumi Ichinose3, Yujirou Uchida3, Hiroyuki Wariishi3, Miho Ohta4 and Toshiyuki Sakaki1

1Department of Biotechnology, Faculty of Engineering, Toyama Prefectural University, 5180 Kurokawa, Imizu, Toyama 939-0398, Japan
2Bioresource Laboratories, Mercian Corp., Iwata-shi, Shizuoka, Japan.
3Department of Forest and Forest Products Sciences, Graduate School of Bioresource and Bioenvironmental Sciences, Kyushu University, Fukuoka 812-8581, Japan.
4Department of Food and Nutrition Management Studies Faculty of Human Development, Soai University, 4-4-1 Nanko-naka, Suminoe-ku, Osaka 559-0033, Japan

*To whom correspondence should be addressed: Toshiyuki Sakaki: +81-766-56-7500. +81-766-56-2498. E-mail: tsakaki{at}pu-toyama.ac.jp

Received July 24, 2009; Accepted September 3, 2009


  Abstract

We cloned full-length cDNAs of 130 cytochrome P450s (P450s) derived from Phanerochaete chrysosporium, and successfully expressed 70 isoforms in Saccharomyces cerevisiae. To elucidate substrate specificity of Phanerochaete chrysosporium P450s, we examined various substrates including steroid hormones, several drugs, flavonoids, and polycyclic aromatic hydrocarbons using the recombinant S. cerevisiae cells. Of these P450s, two CYPs designated as PcCYP50c and PcCYP142c with 14% identity in their amino acid sequences catalyze 3’-hydroxylation of flavone and O-deethylation of 7-ethoxycoumarin. Kinetic data of both enzymes on both reactions fitted not to the Michaelis-Menten equation but to Hill's equation with a coefficient of 2, suggesting that two substrates bind to the active site. Molecular modeling of PcCYP50c and a docking study of flavone to its active site supported this hypothesis. The enzymatic properties of PcCYP50c and PcCYP142c resemble mammalian drug-metabolizing P450s, suggesting that their physiological roles are metabolism of xenobiotics. It is noted that these unique Phanerochaete chrysosporium P450s have a potential for production of useful flavonoids.


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