Limonoid metabolism

Table IV. Limonoid-metabolizing Bacteria and Metabolic Pathways...

Other benefits of large numbers of analogs to plants may include slower evolution of tolerance or lower rates of metabolism of mixtures compared with that of single compounds in herbivorous insects. Feng and Isman (1995) investigated the possibility of adaptation in herbivores by repeated selection of peach aphid colonies with either pure azadirachtin or neem seed extracts containing a large number of limonoids. The colonies treated with azadirachtin soon showed evidence of tolerance of this pure compound, whereas no evidence of tolerance was... 

Metabolism in Bacteria. Three species of bacteria, which are capable of metabolizing limonoids, have been isolated from soil by Hasegawa et al. (16,17,18,19), Table IV. 

Metabolism in Citrus. Recently, Hasegawa et al. (6) have established the presence of a deoxylimonoid pathway in Citrus. Methyl-14c VIII was metabolized in leaves of calamondin to form a deoxy derivative, showing the presence of epoxidase activity which is required for the first step of the deoxylimonoid pathway. Compound XVIII, the product of the second step, was also isolated from grapefruit seeds (6). Furthermore, deoxylimonate A-ring lactone hydrolase, which is involved in the third step of the pathway, was also detected in grapefruit seeds (6). These findings clearly show that limonoids are metabolized in Citrus not only via the 17-dehydrolimonoid pathway as previously established (22), but also via the deoxylimonoid pathway. 

A. Hasegawa, S. Metabolism of limonoids Limonin D-ring lactone hydrolase activity in Pseudomonas. J. Agri. Food Chem., 1976, 2A, 2A-26. 

Biological Removal Six species of bacteria, each capable of metabolizing limonoids, have been isolated from soil by enrichment using limonoids as carbon sources. They are Arthrobacter globiformis (34), Pseudomonas 321-18 (35), Arthrobacter globiformis II (36), Bacterium 342-152-1, Corynebacterium fasclans (37) and Aclnetobacter sp. (38). Based on the metabolites and enzymes produced by these species of bacteria, five metabolic pathways of limonoids have been established in bacteria (3)(Fig. 4). 

Biosynthesis and metabolism of limonin and its closely related limonoids... 

Limonoid UDP-D>glucose transferase Limonin bitterness is a problem in juices extracted from early-season to mid-season winter fruit, but not a problem in juice extracted from the late season fruit. As the fruit ripens, the concentration of limonoate A-ring lactone (2) decreases (23,24). This natural limonin debittering process has been known for over a century, but the mechanism of this metabolism was not understood until the recent discovery that limonoid glucosides are present in mature fruit tissues and seeds. We observed that in navel orange the initial... 

Two major groups of metabolically altered tiiterpenes, the limonoids (tetranortriterpenoids) and the quassinoids (decanortriterpenoids) are derived from euphol (1) (Fig. 25.1) or tirucallol (2) (Fig. 25.2). To date, these compounds are restricted in distribution to the Rutaceae, Meliaceae, Cneora-ceae, Simaroubaceae, and, perhaps, the Burseraceae (Connolly and Hill, 1991), and occur variously in seeds, fruits, and wood of plants of these families. In general, the limonoid and quassinoid content of leaves has not been examined (Taylor, 1983). 

Hahlbrock K, Scheel D (1989) Physiology and molecular biology of phenylpropanoid metabolism. Annu Rev Plant Physiol Plant Mol Biol 40 347-369 Hasegawa S, Herman Z (1992) Biosynthesis of limonoids in Citrus. In Petroski RJ, McCormick SP (eds) Secondary-metabolite biosynthesis and metabolism. Plenum Press, New York, pp 305-317... 

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