Bacteria and Plants

In humans, there is no evidence of a nickel deficiency syndrome or proof that nickel is essential. Cows (Bos sp.) fed nickel-deficient diets containing less than 100.0 p.g Ni/kg ration had reduced growth and survival. Nickel-deficiency in cows was exacerbated 

0 mg Ni/kg ration. Lambs given diets containing 65.0 xg Ni/kg DW ration had dismpted metabolism. 

0 (xg Ni/kg ration had inaeased perinatal morality, unthrifty appearance of young rats, deaeased physical activity, deaeased liver cholesterol, and liver histopathology when compared to controls fed diets containing 

In birds, mortality occurred in young individuals of sensitive species when rations contained more than 500.0 mg Ni/kg. Nickel accumulated in avian tissues at dietary loadings as low as 0.7-12.5 mg Ni/kg ration however, nickel intoxication in some species tested was not always reflected by elevated tissue nickel concentrations. 

In mammals, the toxicity of nickel is a function of the chemical form of nickel, dose, and route of exposure. Exposure to nickel by inhalation, injection, or cutaneous contact is more significant than oral exposure. Toxic effects of nickel to humans and laboratory mammals are reported for respiratory, cardiovascular, gastrointestinal, hematological, musculoskeletal, hepatic, renal, dermal, ocular, immunological, developmental, neurological, and reproductive systems. 

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Biotin is produced by a multistep pathway in a variety of fungi, bacteria, and plants (50—56). The estabUshed pathway (50,56) in E. coli is shown in Figure 6. However, Htde is known about the initial steps that lead to pimelyl-Co A or of the mechanism of the transformation of desthiobiotin to biotin. Pimelic acid is beheved to be the natural precursor of biotin for some microorganisms (51). 

The enzymes that catalyze formation of acetyl-ACP and malonyl-ACP and the subsequent reactions of fatty acid synthesis are organized quite differently in different organisms. We first discuss fatty acid biosynthesis in bacteria and plants, where the various reactions are catalyzed by separate, independent proteins. Then we discuss the animal version of fatty acid biosynthesis, which involves a single multienzyme complex called fatty acid synthase. 

The individual steps in the elongation of the fatty acid chain are quite similar in bacteria, fungi, plants, and animals. The ease of purification of the separate enzymes from bacteria and plants made it possible in the beginning to sort out each step in the pathway, and then by extension to see the pattern of biosynthesis in animals. The reactions are summarized in Figure 25.7. The elongation reactions begin with the formation of acetyl-ACP and malonyl-ACP, which... 

The next three steps—reduction of the carbonyl to an alcohol, dehydration to yield a trans-a,(i double bond, and reduction to yield a saturated chain— are identical to those occurring in bacteria and plants (Figure 25.7) and... 

Until the discovery in 1975 of nickel in jack bean urease (which, 50 years previously, had been the first enzyme to be isolated in crystalline form and was thought to be metal-free) no biological role for nickel was known. Ureases occur in a wide variety of bacteria and plants, catalyzing the hydrolysis of urea,... 

In 1973, the first naturally occurring isobacteriochlorin, iron-containing siroheme, was isolated1 from a sulfite reductase of Escherichia coli. Later it was also discovered in sulfite and nitrite reductases of numerous bacteria and plants.2 Iron-free sirohydrochlorins (also called factor II) were discovered in vitamin B12 producing bacteria.3-4 Together with factor III. a sirohydrochlorin methylated in the 20-position, the reduced forms of factor II and factor III were identified as biosynthetic intermediates in the biosynthesis of vitamin B12.5... 

In bacteria and plants, the individual enzymes of the fatty acid synthase system are separate, and the acyl radicals are found in combination with a protein called the acyl carrier protein (ACP). However, in yeast, mammals, and birds, the synthase system is a multienzyme polypeptide complex that incorporates ACP, which takes over the role of CoA. It contains the vitamin pantothenic acid in the form of 4 -phosphopan-tetheine (Figure 45-18). The use of one multienzyme functional unit has the advantages of achieving the effect of compartmentalization of the process within the cell without the erection of permeability barriers, and synthesis of all enzymes in the complex is coordinated since it is encoded by a single gene. 

We have chosen carotenoid biosynthesis as the example system for demonstrating the prospects of biotechnology of food colorants for several reasons. Carotenoid biosynthesis is the second most understood system. Multiple examples of valuable food colorant engineering in fungi, bacteria, and plants have been reported. Finally, carotenogenesis in cereal crops such as maize and rice is the primary focus of our research efforts. Hopefully, we provide the food technologist with a template with which to examine other industrially important pigment systems. 

In a series of papers, Cook et al.60-63 presented results of the 31P NMR studies of pyridoxal 5 -phosphate dependent enzyme. O-acetylserine sulf-hydrylase is the enzyme which catalyses the final step of biosynthesis of l-cysteine, the replacement of p-acetoxy group of O-acetyl-L-serine by thiol [30] in bacteria and plants. 

Vanadium, as V0S04, has been found to interfere with siderophore-mediated iron transport in bacteria and plants. This seems to imply that vanadium can be transported by siderophores, and a number of studies focussing on applications of hydroxamate V-complexes in biology have been initiated. 

Deoxy-araWno-heptulosonic acid 7-phosphate (10) is a metabolic intermediate before shikimic acid in the biosynthetic pathway to aromatic amino-acids in bacteria and plants. While (10) is formed enzymically from erythrose 4-phosphate (11) and phosphoenol pyruvate, a one-step chemical synthesis from (11) and oxalacetate has now been published.36 The synthesis takes place at room temperature and neutral pH... 

To the best of our knowledge, there is one host which conforms to the structure of an Archimedean dual. Harrison was the first to point out that the quaternary structure of ferritin, a major iron storage protein in animals, bacteria, and plants, corresponds to the structure of a rhombic dodecahedron. [45] This protein, which is approximately 12.5 nm in diameter, consists of 24 identical polypeptide subunits (Fig. 9.18), and holds up to 4500 iron atoms in the form of hydrated ferric oxide with... 

L-Rhamnose isomerase catalyzes the interconversion of L-rhamnose and L-rhamnulose. L-Rhamnose, a deoxy sugar, is found in bacteria and plants and it plays an essential role in many pathogenic bacteria. The pathway for the metabolism of this sugar does not exist in humans, and this makes enzymes of this pathway attractive targets for therapeutic intervention. " Rhamnose isomerase from E. coli is a tetramer of (/ /a)8-barrels similar to xylose... 

Histamine is found in animal tissues and venoms and in many bacteria and plants. Within the human body, the... 

Histamine is found in most of the tissues, present in various biological fluids. In most tissues, histamine exists in bound form in granules, in mast cells or basophils. These mast cells are especially rich at sites of potential tissue injury i.e. skin, lungs, liver, GIT etc. and is unevenly distributed. It is also present in many venoms (of bees wasps), bacteria and plant tissues. 

Several mechanisms have evolved to prevent this catastrophe. In bacteria and plants, the plasma membrane is surrounded by a nonexpandable cell wall of sufficient rigidity and strength to resist osmotic pressure and prevent osmotic lysis. Certain freshwater protists that live in a highly hypotonic medium have an organelle (contractile vacuole) that pumps water out of the cell. In multicellular animals, blood plasma and interstitial fluid (the extracellular fluid of tissues) are maintained at an osmolarity close to that of the cytosol. The high concentration of albumin and other proteins in blood plasma contributes to its osmolarity. Cells also actively pump out ions such as Na+ into the interstitial fluid to stay in osmotic balance with their surroundings. 

Carbohydrates are the most abundant biomolecules on Earth. Each year, photosynthesis converts more than 100 billion metric tons of C02 and H20 into cellulose and other plant products. Certain carbohydrates (sugar and starch) are a dietary staple in most parts of the world, and the oxidation of carbohydrates is the central energy-yielding pathway in most nonphotosynthetic cells. Insoluble carbohydrate polymers serve as structural and protective elements in the cell walls of bacteria and plants and in the connective tissues of animals. Other carbohydrate polymers lubricate skeletal joints and participate in recognition and adhesion between cells. More complex carbohydrate polymers covalently... 

FIGURE 21-7 Structure of fatty acid synthases. The fatty acid synthase of bacteria and plants is a complex of at least seven different polypeptides. In yeast, all seven activities reside in only two polypeptides the vertebrate enzyme is a single large polypeptide. 

In bacteria and plants, glutamate is produced from glutamine in a reaction catalyzed by glutamate synthase. a-Ketoglutarate, an intermediate of the citric acid cycle, undergoes reductive amination with glutamine as nitrogen donor ... 

Organisms vary greatly in their ability to synthesize the 20 common amino acids. Whereas most bacteria and plants can synthesize all 20, mammals can synthesize only about half of them—generally those with simple pathways. These are the nonessential amino acids, not needed in the diet (see Table 18-1). The remainder, the essential amino acids, must be obtained from food. Unless otherwise indicated, the pathways for the 20 common amino acids presented below are those operative in bacteria. 

HGURE 22-16 Biosynthesis of chorismate, an intermediate in the synthesis of aromatic amino acids in bacteria and plants. 

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