Marine organism sources

Bioturbating activities of some benthic marine organisms. Source. From Pearson, T. H. Rosenberg (1976). Ambio, 5, 79. 

Rich sources of vitamin A include dairy products such as milk cheese, butter, and ice cream. Eggs as well as internal organs such as the Hver, kidney, and heart also represent good sources. In addition, fish such as herring, sardines, and tuna, and in particular the Hver oil from certain marine organisms, are excellent sources. Because the vitamin A in these food products is derived from dietary carotenoids, vitamin A content can vary considerably. Variation of vitamin A content in food can also result from food processing and in particular, oxidation processes (8). 

The underlying assumption driving marine natural products chemistry research is that secondary metabolites produced by marine plants, animals, and microorganisms will be substantially different from those found in traditional terrestrial sources simply because marine life forms are very different from terrestrial life forms and the habitats which they occupy present very different physiological and ecological challenges. The expectation is that marine organisms will utilize completely unique biosynthetic pathways or exploit unique variations on well established pathways. The marine natural products chemistry research conducted to date has provided many examples that support these expectations. 

Fatty acids with odd numbers of carbon atoms are rare in mammals, but fairly common in plants and marine organisms. Humans and animals whose diets include these food sources metabolize odd-carbon fatty acids via the /3-oxida-tion pathway. The final product of /3-oxidation in this case is the 3-carbon pro-pionyl-CoA instead of acetyl-CoA. Three specialized enzymes then carry out the reactions that convert propionyl-CoA to succinyl-CoA, a TCA cycle intermediate. (Because propionyl-CoA is a degradation product of methionine, valine, and isoleucine, this sequence of reactions is also important in amino acid catabolism, as we shall see in Chapter 26.) The pathway involves an initial carboxylation at the a-carbon of propionyl-CoA to produce D-methylmalonyl-CoA (Figure 24.19). The reaction is catalyzed by a biotin-dependent enzyme, propionyl-CoA carboxylase. The mechanism involves ATP-driven carboxylation of biotin at Nj, followed by nucleophilic attack by the a-carbanion of propi-onyl-CoA in a stereo-specific manner. 

Iodine occurs as iodide ions in brines and as an impurity in Chile saltpeter. It was once obtained from seaweed, which contains high concentrations accumulated from seawater 2000 kg of seaweed produce about 1 kg of iodine. The best modern source is the brine from oil wells the oil itself was produced by the decay of marine organisms that had accumulated the iodine while they were alive. Elemental iodine is produced by oxidation with chlorine ... 

Because chitin is the most abundant compound of nitrogen, it represents the major source of nitrogen accessible to countless Uving terrestrial and marine organisms. 

M Diatoms constitute a family of unicellular microscopic algae whose cell walls consist of two boxlike parts which contain silica. They are an important source of food for all kinds of marine organisms. 

Marine organisms frequently contain a complex mixture of sterols. The biosynthetic origin of these compounds is complicated by the fact that there are four possible sources. The sources by which marine invertebrates may obtain sterols, first described by Goad [3], are (1) de novo biosynthesis, (2) assimilation from diet, (3) modification of dietary sterols and (4) assimilation of symbiont-produced sterols or sterol precursors. In any examination of the biosynthetic origin(s) of sterols one must consider all of these factors needless to say, a complex picture is emerging. 

Ecological Analysts, Inc. 1981. The Sources, Chemistry, Fate, and Effects of Chromium in Aquatic Environments. (Avail, from American Petroleum Institute, 2101 L St., N.W., Washington, D.C. 20037. 207 pp.) Eisler, R. 1981. Trace Metal Concentrations in Marine Organisms. Pergamon Press, NY. 687 pp. 

TABLE 4.2 Selected Solid Reference Materials Currently Available from Canadian, U.S., and European Sources with Potential Utility for Marine Organic Studies (See Appendix E for information about obtaining these materials.)... 

Isotopes as Tracers of the Source and Fate of Marine Organic Compounds... 

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