Professor and Natural Products Chemist
232 Hilgard Hall
Phone #: (510) 643-6303
FAX #: (510) 643-0215
Our group has been searching for ecologically sound pest control agents
based on natural products (including biopolymers such as enzymes) that fundamentally
regulate nature. Our studies have focused on developing alternative insect
control agents, but the scope has now extended to microorganisms and weeds.
A number of biologically active natural products have been isolated but
only a few are useful to us as pest control agents. This is mainly due to
the lack of their rational exploration, even though understanding their
effects on biological systems and the biochemical changes involved are known
to be essential. For example, plant resistance to pests usually involves
combinations of compounds, many of them short-lived. Their dynamic analysis
and functional understanding are needed. Our group has been pursuing this
type of study.
Based on our observation during a simple lettuce seedling assay, we found
that the lettuce exuded a polyphenol oxidase (PPO) from the roots of the
seedlings into the rhizosphere. This can be visualized when an exogenous
substrate such as catechin is present in the test solution, the root caps
and solution surrounding the roots are stained yellow to orange. Thus, the
enzyme exuded from the root of lettuce seedlings oxidizes catechin although
the corresponding o-quinone has not yet been characterized. In addition
to lettuce, a number of crops such as tomato, alfalfa, corn and wheat also
exude PPOs that are membrane-bound copper containing glycoproteins. The
role of the PPO exuded from lettuce seedling, as well as other plants, may
be a line of passive defense against soil microorganisms and insects. This
led us to investigate the role of PPO, using a series of simple phenolic
compounds as a model in order to gain new insights into their actions on
a molecular basis. The enzyme has been isolated from the lettuce exudate
and its structural characterization is underway. This study has been extended
to a similar oxidase present in insects known as tyrosinase because it is
one of the key enzymes in the insect molting process. We have reported that
ecdysteroid-22-O-acyltransferase in the tobacco budworm, Heliothis virescens
plays an important role as a line of defense against exogenous ecdysteroids.
Accumulation of this kind of knowledge may provide clues to design more
Another aspect of our research is identifying the antimicrobial activity
of natural products. This ongoing project has begun to encompass the underlying
rationale for structure-antimicrobial activity relationships.
Zhang, M. and Kubo, I. 1993. Metabolic fate of ecdysteroids in larval Bombyx
mori and Heliothis virescens. Insect Biochem. Molec. Biol. 23:831-843.
Zhang, M., Chaudhuri, S.K., and Kubo, I. 1993. Quantification of insect
growth and its use in screeming of naturally occurring insect control agents.
J. Chem. Ecol 19:1107-1118.
Kubo, I., Muroi, H., and Kubo, A. 1995. Structural functions of antimicrobial
long-chain alcohols and phenols. Bioorg. Med. Chem. 3:873-880.
Kubo, I., Jamalamadaka, V., Kamikawa, T., Takahashi, K., Tabata, K., and
Kusumi, T. 1996. Absolute stereochemistry of tanabalin, an insect antifeedant
clerodane from Tanacetum balsamita. Chem. Lett. 441-442.
Muroi, H. and Kubo, I. 1996. Bacterial activity of anacardic acid and totarol,
alone and in combination with methicillin, against methicillin-resistant
Staphylococcus aureus. J. Appl. Bacteriol.80:387-394.
Current Graduate Students:
- David G. Hammond
- Christopher S. Lunde
- Brice A. McPherson
- Sang Hwa Lee
- Ikuyo Kinst-Hori