Enzymes marine organism

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. 

Isonitriles are widespread metabolites in marine organisms, although little attention has been paid to their degradation. Pseudomonas putida strain N-19-2 can hydrolyze isonitriles to N-substituted formamides (Goda et al. 2001), and the enzyme is active toward cyclohexyl isonitrile and benzyl isonitrile. 

Many marine organisms have enzymes called haloperoxidases that convert nucleophilic iodide, bromide, or chloride anions into electrophilic species that react like I+, Br+ or Cl+. 

Simply on the basis of the normal composition of marine organisms, we would expect proteins and peptides to be normal constituents of the dissolved organic carbon in seawater. While free amino acids might be expected as products of enzymic hydrolysis of proteins, the rapid uptake of these compounds by bacteria would lead us to expect that free amino acids would normally constitute a minor part of the dissolved organic pool. This is precisely what we do find the concentration of free amino acids seldom exceeds 150 xg/l in the open ocean. It would be expected that the concentration of combined amino acids would be many times as great. There have been relatively few measurements of proteins and peptides, and most of the measurements were obtained by measuring the free amino acids before and after a hydrolysis step. Representative methods of this type have been described [245-259]. Since these methods are basically free amino acid methods, they will be discussed next in conjunction with those methods. 

Reviews on the fate of aromatic hydrocarbons in marine organisms have been published (2,3,4). They indicated that a substantial amount of information exists on the accumulation of these compounds in a variety of phylogenetically diverse organisms. Recently, emphasis has shifted toward studies of bioconversions of these hydrocarbons. Work has been conducted on enzymes mediating the degradation of aromatic hydrocarbons and on the formation and retention of metabolites. Identifications of individual metabolites in tissues and body fluids of several marine organisms exposed to radiolabeled aromatic hydrocarbons have been made however, insufficient information is available to determine the extent of differences in metabolite profiles as evinced from chromatographic data. 

Enzymes of the hepatic microsomes of most marine organisms, with the notable exception of certain molluscs, metabolize xeno-biotic substrates however, as much as 600-fold variations in enzyme activities have been noted between different species of marine teleosts (40). The hepatic enzyme activities of aquatic species are generally lower, with most substrates tested, than the hepatic enzymes of mammals (40). The mixed function oxidase enzymes in marine organisms are inducible by hydrocarbons, such as 3-methylcholanthrene or benzo[a]pyrene. Moreover, it is known... 

In Chapter 4, we saw how conservative chemicals are used to trace the pathway and rates of water motion in the ocean. True conservative behavior is exhibited by a relatively small number of chemicals, such as the major ions and, hence, salinity. In contrast, most of the minor and trace elements display nonconservative behavior because they readily undergo chemical reactions under the environmental conditions found in seawater. The rates of these reactions are enhanced by the involvement of marine organisms, particularly microorganisms, as their enzymes serve as catalysts. Rates are also enhanced at particle interfaces for several reasons. First, microbes tend to have higher growth rates on particle surfaces. Second, the solution in direct contact with the particles tends to be highly enriched in reactants, thereby increasing reaction probabilities. Third, adsorption of solutes onto particle surfaces can create fevorable spatial orientations between reactants that also increases reaction probabilities. 

Marine organisms concentrate metals in their tissues and skeletal materials. Many of these trace metals are classified as micronutrients because they are required, albeit in small amounts, for essential metabolic functions. Some are listed in Table 11.4, illustrating the role of metals in the enzyme systems involved in glycolysis, the tricarboxylic acid cycle, the electron-transport chain, photosynthesis, and protein metabolism. These micronutrients are also referred to as essential metals and, as discussed later, have the potential to be biolimiting. 

Although surfece waters are supersaturated with respect to calcium carbonate, abiogenic precipitation is imcommon, probably because of unfevorable kinetics. (The relatively rare formation of abiogenic calcite is discussed further in Chapter 18.) Marine organisms are able to overcome this kinetic barrier because they have enzymes that catalyze the precipitation reaction. Because fl declines with depth, organisms that deposit calcareous shells in deep waters, such as benthic foraminiferans, must expend more energy to create their hard parts as compared to surfece dwellers. 

Amino acids become linked by reactions that occur between the amine group of one amino acid and the carboxyl group of another. As shown in Figure 22.23, this polymerization produces a molecule of water and, hence, is a condensation reaction. Naturally occurring polypeptides with molecular weights in excess of 10,000 daltons are termed proteins. These biomolecules are ubiquitous in marine organisms and are not specific to particular species. Proteins are important components of enzymes as well as of structural parts and connective tissues. 

Fig. 5. The reaction of ethanolamine-phosphate cytidylytransferase with substrates and analogues. Reaction 1 shows the normal reaction of the enzyme with ethanolamine phosphate (2-aminoethyl phosphate), which is part of the route of phospholipid synthesis. The alternative reaction with 2-aminoethylphosphonate, in parentheses, is used by some marine organisms to insert a C—P bond into their phospholipids. Reaction 2 shows the futile cycle obtained with 2-aminoethylarsonate (59). The symbol -P signifies -P03H2 and its ionized forms, and -P- signifies -P(0)(0H)- and its ionized form (61).

Owing to the immense diversity of animals and microbes in the marine environments, and their almost untouched capacity to produce natural products, the importance for marine pharmaceutical and nutra-ceutical industries was realized on a broad basis by the scientific communities recently. This has strengthened worldwide research activities on the exploration of bioactive compounds from marine organisms for pharmaceutical use, as well as the development of other valuable products, such as enzymes, nutraceuticals, and cosmeceuticals. 

A similar cleavage is catalyzed by thiamin-degrading enzymes known as thiaminases which are found in a number of bacteria, marine organisms, and plants. 

Marine organisms are a well-established source of unique and biologically active peptides. Complex cyclic peptides and depsipeptides have emerged as an important new class of metabolites present in extracts of marine organisms. Many of these peptides have been found to be extremely potent cytotoxic and /or enzyme inhibitors. 

Besides sponges and algae, enzymes were also isolated from marine organisms and microorganisms. For example, polymerases and proteases from marine Vibrio sp. [352], marine bacterium such as Alcaligenes faecalis [353], and from archaeons, such as the psychrophilic Cenarchaeum symbiosum [354], and the hyperthermophile archaeons Pyrococcus furiosus [355], Sulfolobus solfataricus [356], and Aeropyrum pernix [357] transferases from marine bacterium such as Vibrio vulnificus... 

Early studies revealed that the 3, 5 -cyclic phosphate diesterase is present in all mammalian tissues (38, 33, 36), being most active in cerebral cortex (36, 37). It has also been identified in extracts of liver fluke (Fasciola hepatica), the common earthworm (Lumbricus terrestris), and fly larvae (36) and it has been studied in marine organisms (38), the cellular slime mold Dictyostelium discovdeum (39, AO), and in E. coli (Al). The enzyme has been partially purified from beef heart (30), dog heart, (A8) and bovine brain (37, A3). No highly purified preparations have yet been obtained and most studies have been performed with relatively crude preparations. 

In cases where environmental factors appear to influence the biosynthetic outcomes in a marine organism, it becomes desirable to comprehend how the biosynthetic pathway is regulated at the molecular level. The biosynthetic switching on and off of genes that express individual enzymes, when better understood, will also aid environmentally sound production of marine metabolites for pharmaceutical or biotechnological use. 

---