Defensive metabolites

Secondary Metabolite Defenses Against Pathogens and Biofoulers... 

In spite of a rich life, no signaling or defensive secondary metabolite has ever been reported from organisms thriving on the hydrothermal vents. Lack of competition in these areas, where the hostile environment provides protection from invaders, has not stimulated the formation of defensive metabolites. Defensive heat-stable enzymes and cell walls were raised against the hostile environment. 

Many plant families have different biosynthetic groups of secondary metabolite defenses, and their possible interaction in plant defense has received little attention. The Asteraceae (daisy family) presents several characteristic groups of widely... 

Bristol-Myers Squibb tried a similar metabolite defense three times in 1999 and 2000 for its antianxiety pill BuSpar, which was due to go off patent in November 2000. 

Substituting EPI for DOX Lower formation of ROS or secondary alcohol metabolite Same as those of DOX combination with drugs that stimulate anthracycline conversion to secondary alcohol metabolite or diminish the cardiac defenses against ROS... 

Cellular defense mechanisms against toxins (A multistep mechanism for elimination of toxic metabolites and xenobiotics. It involves various transport, oxidation, and conjugation steps.) are usually divided into several steps as it is visualized on Fig. 3. Organic anion transporting proteins (OATPs) are responsible for the cellular uptake of endogenous compounds and... 

Hiraishi, H., Razandi, M., Terano, A. and Ivey, K.J. (1990). Antioxidant defenses of culture gastric mucosal cells against toxic oxygen metabolites. Role of glutathione redox cycle and endogenous catalase. Gastroenterology 98, A544. 

The following sections summarize our sparse knowledge about chemical defense in plankton and outlines the role that defensive metabolites can play in this ecosystem. 

Other roles for noxious metabolites produced by certain phytoplankton species include mediation of allelopathic interactions [47]. Allelopathy covers biochemical interactions among different primary producers or between primary producers and microorganisms. These can provide an advantage for the producer in the competition among different photoautotrophs for resources. Although not directly involved in chemical defense, allelopathic metabolites can affect the dominance and succession of species in phytoplankton therefore they are crucial for understanding plankton composition. In contrast to the fresh water environment, the location of many studies on the role of allelopathic interactions, which have identified active compounds [47], only few studies have addressed this topic in the marine environment. 

One or a few enzymes usually mediate the conversion slight structural changes in the metabolites can markedly enhance potency of chemical defenses... 

The role of antiproliferative effects of an activated defense reducing the next generation of herbivores compared with the straightforward action of toxins or feeding deterrent metabolites in the evolutionary arms race is still under discussion. The proposed mechanism suggests natural selection at the group level,... 

Only a few studies on defined chemical defense metabolites from non-phyto-plankton organisms that spend their entire life history in the water column have been reported to date [81]. 

One example for a chemically defended zooplankton species is the Antarctic pteropod Clione antarctica. This shell-less pelagic mollusk offers a potentially rich source of nutrients to planktivorous predators. Nonetheless fish do not prey on this organism, due to its efficient chemical defense. In a bioassay-guided structure elucidation, pteroenone 37 could be isolated and characterized as the main defensive principle of C. antarctica [82,83]. If embedded in alginate, this compound is a feeding-deterrent in nanomolar concentrations. This unusual metabolite is likely to be produced by C. antarctica itself and not accumulated from its food, since its major food sources did not contain any detectable quantities of 37. 

Meroplankton comprise organisms that spend only part of their life in the plankton. Primarily eggs and larvae of benthic or actively swimming adults fulfill this criterion, and the study of their chemical defense is often supported by the knowledge of defensive metabolites of their adult life stages. 

Scheme 11 Halogenated aromatic metabolites involved in the chemical defense of the polychaete Capitella sp.

In contrast to our sparse knowledge about the action of chemicals as defense in plankton, the identified metabolites with defined defensive activities from benthic organisms are numerous. Nearly every habitat from the Antarctic [94] to coral reefs [95] has been extensively investigated - often motivated by the... 

The ability to respond so rapidly should be advantageous when herbivoregrazing is intense but extremely variable over short periods of time. The defense on demand could thus result in high levels of the defensive metabolites halimedatrial (50) and the unstable epihalimedatrial (51) only in the presence of actively feeding herbivores. Since grazing was also reduced significantly more by purified halimedatrial (50) than by halimedatetraacetate (48) this reaction fulfills all three criteria defined for a wound-activated defense (see above). 

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