Animal metabolism

The presence of nucleic acids ia yeast is oae of the maia problems with their use ia human foods. Other animals metabolize uric acid to aHantoia, which is excreted ia the uriae. Purines iagested by humans and some other primates are metabolized to uric acid, which may precipitate out ia tissue to cause gout (37). The daily human diet should contain no more than about 2 g of nucleic acid, which limits yeast iatake to a maximum of 20 g. Thus, the use of higher concentrations of yeast proteia ia human food requires removal of the nucleic acids. Unfortunately, yields of proteia from extracts treated as described are low, and the cost of the proteia may more than double. 

In animal metabolism, oxomolybdoenzymes catalyse a number of oxidation processes. These oxidases contain Mo coordinated to terminal O and S atoms, and their action appears to involve loss of an O or S atom along with reduction to Mo or Mo". It is, however, the role of molybdenum in nitrogen fixation which has received most attention. 

Copper is essential in animal metabolism. In some animals, such as the octopus and certain arthropods, it transports oxygen through the blood, a role performed by iron in mammals. As a result, the blood of these animals is green rather than red. In mammals, copper-bearing enzymes are necessary for healthy nerves and connective tissue. 

To select and define the target analytes for the residue analysis of crops in a field trial, applicants should consider metabolites/degradation products of the test materials by conducting plant and animal metabolism studies and by assessing toxicity of the metabolites/degradation products. 

The toxic effects of selected plant analytes will be assessed by comparison with the toxicides of similar metabolites found in animal metabolism studies. The amount of the analytes reported in the plant metabolism study is one of the important factors used to establish the residue definition. 

J.E. Dalidowicz, T.D. Thomson, and G.E. Babbitt, Ractopamine hydrochloride, a phenethanolamine repartitioning agent, in Xenobiotics in Food Producing Animals Metabolism and Residues, ed. D.H. Hutson, D.R. Hawkins, G.D. Paulson, and C.B. Stru-ble, American Chemical Society, Washington, DC, Chapter 16, pp. 234-243 (1992). 

Arts. (a) Urea is a product of animal metabolism and thiourea is its sulfur analog, (b) Both hydrogen atoms of their parent, formaldehyde, H2CO, have been replaced with amino groups, and there arc no C—C or C—H bonds left. 

Clarification of copper interactions with molybdenum, sulfate, iron, and zinc in plant and animal metabolisms (NAS 1977 Eisler 1989, 1993)... 

Diflubenzuron breakdown by hydrolysis, soil degradation, or plant and animal metabolism initially yields 2,6-difluorobenzoic acid and 4-chlorophenylurea. Ultimately, the end products are... 

These in vivo and in vitro human metabolism studies indicate that pyrethroids undergo rapid metabolism and elimination as observed in rats, and qualitative metabolic profiles (e.g., kinds of metabolites) of pyrethroids are assumed to be almost the same between humans and rats, suggesting that a large database of animal metabolism of pyrethroids could provide useful information for the evaluation of behavior of pyrethroids in humans. Nowadays, human pesticide dosing studies for regulatory propose are severely restricted in the US, and thus detailed comparison of in vitro metabolism (e.g., metabolic rate constants of pathways on a step-by-step basis) using human and animal tissues could be an appropriate method to confirm the similarity or differences in metabolism between humans and animals. 

Because the role of inositol in animal metabolism complies with the definition of vitamin, it is usually included in this class of substances, although the quantities and concentrations involved are of much higher magnitude. 

Is the effect reversible Reversibility of a response is dependent on the drug itself, exposure levels/duration, and factors related to the test animal (metabolic capability, genetic susceptibility, etc.). Most effects produced by immunosuppressive drugs have been shown to be reversible after cessation of therapy, such as those produced during cancer chemotherapy. However, if a tumor develops before the immune system is restored, the effect is not reversible, as is the case of secondary tumors related to chemotherapy. 

Although previous applications of this technique in our laboratory had been concerned with aquatic animal metabolism of pesticides such as DDT, parathion, carbaryl, and trifluralin (14, 15), we also became interested in comparing metabolic routesljy means of a "metabolic probe". Such a compound ideally should be stable to nonbiological degradation, of low toxicity to maximize the dose, and subject to as many major routes of metabolism as possible without undue analytical complexity. 

Taxol (Paclitaxel) 137, a natural product derived from the bark of the Pacific yew, Taxus brevifolia [213-215], and the hemisynthetic analogue Docetaxel (Taxotere) 138, two recent and promising antitumour agents, have been the matter of extensive in vivo and in vitro animal metabolic studies. The major metabolites of taxol excreted in rat bile [216] were identified as a C-4 hydroxylated derivative on the phenyl group of the acyl side chain at C-13 (139), another aromatic hydroxylation product at the mefa-position on the benzoate group at C-2 (140) and a C-13 deacylated metabolite (baccatin III, 142) the structure of six minor metabolites could not be determined. The major human liver microsomal metabolite, apparently different from those formed in rat [217], has been identified as the 6a-hydroxytaxol (141) [218, 219]. A very similar metabolic pattern was... 

Some rather important indole derivatives influence our everyday lives. One of the most common ones is tryptophan, an indole-containing amino acid found in proteins (see Section 13.1). Only three of the protein amino acids are aromatic, the other two, phenylalanine and tyrosine being simple benzene systems (see Section 13.1). None of these aromatic amino acids is synthesized by animals and they must be obtained in the diet. Despite this, tryptophan is surprisingly central to animal metabolism. It is modified in the body by decarboxylation (see Box 15.3) and then hydroxylation to 5-hydroxytryptamine (5-HT, serotonin), which acts as a neurotransmitter in the central nervous system. 

Sugar alcohols (6) such as sorbitol and mannitol do not play an important role in animal metabolism. 

The natural amino acids are mainly a-amino acids, in contrast to (3-amino acids such as p-alanine and taurine. Most a-amino acids have four different substituents at C-2 (Ca). The a atom therefore represents a chiral center—I e., there are two different enantiomers (L- and D-amino acids see p. 8). Among the proteinogenic amino acids, only glycine is not chiral (R = H). In nature, it is almost exclusively L-amino acids that are found. D-Amino acids occur in bacteria—e. g., in murein (see p.40)—and in peptide antibiotics. In animal metabolism, D-Amino acids would disturb the enzymatic reactions of L-amino acids and they are therefore broken down in the liver by the enzyme D-amino add oxidase. 

Adenosylcobalamin (coenzyme 812) carries a covalently bound adenosyl residue at the metal atom. This is a coenzyme of various isomerases, which catalyze rearrangements following a radical mechanism. The radical arises here through homolytic cleavage of the bond between the metal and the adenosyl group. The most important reaction of this type in animal metabolism is the rearrangement of methylmalonyl-CoAto form succinyl-CoA, which completes the breakdown of odd-numbered fatty acids and of the branched amino acids valine and isoleucine (see pp. 166 and 414). 

Waste products from the degradation of organic substances in animal metabolism include carbon dioxide (CO2), water (H2O), and ammonia (NH3). In mammals, the toxic substance ammonia is incorporated into urea and excreted in this form (see p. 182). 

The degradation of most amino acids is anaplerotic, because it produces either intermediates of the cycle or pyruvate glucogenic amino acids see p. 180). Gluconeogenesis is in fact largely sustained by the degradation of amino acids. A particularly important anaplerotic step in animal metabolism leads from pyruvate to oxaloacetic acid. This ATP-dependent reaction is catalyzed by pyruvate... 

By contrast, acetyl CoA does not have anaplerotic effects in animal metabolism. Its carbon skeleton is completely oxidized to CO2 and is therefore no longer available for biosynthesis. Since fatty acid degradation only supplies acetyl CoA, animals are unable to convert fatty acids into glucose. During periods of hunger, it is therefore not the fat reserves that are initially drawn on, but proteins. In contrast to fatty acids, the amino acids released are able to maintain the blood glucose level (see p. 308). 

In the last step, pyruvate kinase transfers this residue to ADP. The remaining enol pyruvate is immediately rearranged into pyruvate, which is much more stable. Along with step [7] and the thiokinase reaction in the tricarboxylic acid cycle (see p. 136), the pyruvate kinase reaction is one of the three reactions in animal metabolism that are able to produce ATP independently of the respiratory chain. 

Oxidative deamination, with the formation of NADH+H only applies to glutamate in animal metabolism. The reaction mainly takes place in the liver and releases NH3 for urea formation (see p. 178). 

Cleavage of fumarate from argininosuc-cinate leads to the proteinogenic amino acid arginine, which is synthesized in this way in animal metabolism. 

In contrast to animals, microorganisms are able to synthesize folate from their own components. The growth of microorganisms can therefore be inhibited by sulfonamides, which competitively inhibit the incorporation of 4-aminobenzoate into folate (see p. 254). Since folate is not synthesized in the animal organism, sulfonamides have no effect on animal metabolism. 

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