Isao Kubo

Professor
PhD  
  

232A Hilgard Hall
Berkeley, California 94720
ikubo@berkeley.edu
office: 510-643-6303   lab: 510-643-6303   fax:  510-643-5438

     Recent publications     

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 appropriate pesticides.

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.

Add here

2-Hydroxy-4-isopropylbenzaldehyde, a potent partial tyrosinase inhibitor. [K. Nihei, Y. Yamagiwa, T. Kamikawa and I. Kubo (2004) Bioorg. Med. Chem. Lett. 14, 681-683]

QSAR and kinetics of the inhibition of benzaldehyde derivatives against Sacrophaga neobelliaria phenoloxidase. [W. Li and I. Kubo (2004) Bioorg. Med. Chem. 12, 701-713]

Hydroquinone, a control agent of agglutination and adherence of Streptococcus mutans induced by sucrose. [M. Himejima, K. Nihei and I. Kubo (2004) Bioorg. Med. Chem. 12, 921-925]

Insect antifeedants from tropical plants: Structures of dumnin and dumsenin. [K. Nihei, Y. Asaka, Y. Mine, C. Ito, H. Furukawa, M. Ju-ichi and I. Kubo (2004) J. Agric. Food Chem. 52, 3325-3328]

Arudonine, an allelopathic steroidal glycoalkaloid from the root bark of Solanum arundo Mattei. [K. Fukuhara, K. Shimizu and I. Kubo (2004) Phytochemistry 65, 1283-1286]

Characterization of xanthine oxidase inhibition by anacardic acids. [N. Masuoka and I. Kubo (2004) Biochim. Biophys. Acta 1688, 245-249]

Lipoxygenase inhibitory activity of octyl gallate. [T. J. Ha, K. Nihei and I. Kubo (2004) J. Agric. Food Chem. 52, 3177-3181]

Identification of oxidation product of arbutin in mushroom tyrosinase assay system. [K. Nihei and I. Kubo (2003) Bioorg. Med. Chem. Lett. 13, 2409-2412]

Tyrosinase inhibitors from galls of Rhus javanica leaves and their effects on insects. [I. Kubo, I. Kinst-Hori, K. Nihei, F. Soria, M. Takasaki, J. S. Calderón and C. L. Céspedes (2003) Z. Naturforsch. C: J. Biosci. 58c, 719-725]

Synergism of polygodial and trans-cinnamic acid on inhibition of root elongation in lettuce seedling growth bioassays. [K. Fujita and I. Kubo. J. Chem. Ecol. 29, 2253-2262 (2003)]

ent-Isopimarane diterpenoids of the leaves from Rabdosia forrestii. [I. Kubo, K. Shimizu, Y-L. Xu (2003) Fitoterapia 74, 643-649]

(+)-2,3-Dehydro-10-oxo-*-isosparteine in Uresiphita reversalis larvae fed on Cytisus monspessulanus leaves. [K. Nihei, K. Shibata and I. Kubo (2002) Phytochemistry 61, 987-990]

Insect antifeedants from tropical plants II: Structure of zumsin. [K. Nihei, F. J. Hanke, Y. Asaka, T. Matsumoto and I. Kubo (2002) J. Agric. Food Chem. 50, 5048-5052]