Invertebrates cytochromes

Mechanistic studies have shown that TBT and certain other forms of trialkyltin have two distinct modes of toxic action in vertebrates. On the one hand they act as inhibitors of oxidative phosphorylation in mitochondria (Aldridge and Street 1964). Inhibition is associated with repression of ATP synthesis, disturbance of ion transport across the mitochondrial membrane, and swelling of the membrane. Oxidative phosphorylation is a vital process in animals and plants, and so trialkyltin compounds act as wide-ranging biocides. Another mode of action involves the inhibition of forms of cytochrome P450, which was referred to earlier in connection with metabolism. This has been demonstrated in mammals, aquatic invertebrates and fish (Morcillo et al. 2004, Oberdorster 2002). TBTO has been shown to inhibit P450 activity in cells from various tissues of mammals, including liver, kidney, and small intestine mucosa, both in vivo and in vitro (Rosenberg and Drummond 1983, Environmental Health Criteria 116). 

Of particular interest in the present context is that TBT can inhibit cytochrome-P450-based aromatase activity in both vertebrates and aquatic invertebrates (Morcillo et al. 2004, Oberdorster and McClellan-Green 2002). The conversion of testosterone to estradiol is catalyzed by aromatase, and so inhibition of the enzyme can, in principle, lead to an increase in cellular levels of testosterone. The significance of this is that many mollusks experience endocrine disruption when exposed to TBTs,... 

Tributyltins and other organotins induce chromosomal aberrations in mammals, although this was not observed in tests with aquatic invertebrates (Dixon and Prosser 1986). Studies with isolated rat hepatoma cells, TBT, and PCB 126, show that TBT inhibits cytochrome P-4501A activity, and PCB 126 induces EROD activity. However, PCB-induced EROD activity was potentiated by coexposure to low noncytotoxic concentrations of TBT (Kannan et al. 1998b). Authors concluded that TBT does not interfere with Ah receptor binding and that potentiation of EROD activity and cytotoxicity as a result of coexposure to PCB 126 and TBT is significant because they coaccumulated in a variety of marine organisms. 

Smital T, Luckenbach T, Sauerborn R, Hamdoun AM, Vega RL, Epel D (2004) Emerging contaminants - pesticides, PPCPs, microbial degradation products and natural substances as inhibitors of multixenobiotic defense in aquatic organisms. Mutat Res 552 101-117 Snyder MJ (2000) Cytochrome P450 enzymes in aquatic invertebrates recent advances and future directions. Aquat Toxicol 48 529-547... 

Even an invertebrate animal that gives no appearance of physical activity possesses a muscle that has a capacity of the Krebs cycle that is similar to that in a muscle of a young adult human. This is the radular retractor muscle of a mollusc, the wheUc. Whelks are found on the seashore they can use their radula continually for very long periods, up to 24 hours in some cases, to rasp flesh off, for example, a fish carcass. A simple dissection of a whelk readily reveals the radular retractor muscle, easily identified by its brilliant red colour. This muscle illustrates the principle that for muscles that are physiologically essential and have to work for long periods of time, the generation of ATP must be from the oxidation of a fuel which requires mitochondria and therefore cytochromes, which is why the radular retractor muscle is red. 

This iron storage protein is widely distributed in many mammalian cells, and also in invertebrates, plants, fungi and a number of bacteria, where it is associated with a fe-type cytochrome. There have been considerable advances recently in the understanding of its structure and physiological function.1093 1098... 

The following discussion will center on mixed-function oxidases involving the hemoprotein cytochrome P-450, the active center of which consists of protoporphyrin IX. Mixed-function oxidases based on cytochrome P-450 are perhaps best known for their role in the primary metabolism of lipophilic xenobiotics in mammals, birds, fish and many invertebrates including insects. While this function is often critical in determining the survival of an organism... 

There are consistent attempts in the literature to interpret specific biotransformation of PCBs that occurred in an organism from the relative ratio of X-CB to that of a reference CB-Y. The later could be CB-153, CB-138 (2,2, 3,4,4, 5-hexa CB), and CB-180 (2,2, 3,4,4, 5,5 -hepta CB) [52]. Such structure-dependent metabolism studies predicted induction of Cytochrome P450 isozymes in the marine food chain [59], small cetaceans [52], beluga and narwhal [60], river dolphins [61], pinnipeds [52], aquatic fauna including invertebrates [62], and in humans [63]. Comprehensive characterization of xenobiotic metabolizing enzymes in whales and pinnipeds has been carried out to show the utility of this approach [51,64]. 

Various other type b cytochromes are found in invertebrates, protozoa, bacteria, fungi, algae and higher plants and reported under the names of cytochrome 6, 5-554, 6-556, 6-557, 6-558, 6-559, 6-560, 6-561, 6-562,... 

Cytochrome 6g-like proteins in housefly and presumably other invertebrates are more easily extractable (usually with simple salt solutions) than the liver cytochrome 65 which is extracted only by the action of proteolytic enzymes or detergents. However, the cytochrome 6-555 (as well as cytochrome 6-563) of the housefly is not extracted from the adult flies with the salt solution (155). 

Several cytochromes typical for invertebrates have been reported under the names helicorubin, enterochrome-566, enterochrome-556 (286,286), and cytochromes h (287-289). The former two pigments are type b cyto-... 

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