Metabolic interrelationships pathways

The metabolic interrelationship between mitochondrial carbamoyl phosphate synthesis to urea formation and to cytosolic carbamoyl phosphate channeled into pyrimidine biosynthesis. In ornithine transcarbamoyiase (OTC) deficiency, mitochondrial carbamoyl phosphate diffuses into the cytosol and stimulates pyrimidine biosynthesis, leading to orotidinuria. Administration of allopurinol augments orotidinuria by increasing the flux in the pyrimidine biosynthetic pathway. CPS = Carbamoyl phosphate synthase, AT = aspartate transcarbamoyiase, D = dihydroorotase, DH = dihydroorotate dehydrogenase, OPRT = orotate phosphoribosyltransferase, XO = xanthine oxida.se,... 

There are several metabolic interrelationships between riboflavin and vitamin Bg. The conversion of pyridoxine or pyridoxamine phosphates to pyri-doxal phosphate is catalyzed by a flavoenzyme (pyri-doxaminephosphate oxidase EC 1.4.3.5), so that a deficiency of riboflavin may, at certain key sites, result in a secondary deficiency in Bg-dependent pathways. More evidence is needed to clarify the extent and importance of these interactions. 

In intact cell systems or vivo, the primary products of a-hydroxylation, 22. have not been detected. The principal urinary metabolites of NNN resulting from a-hydroxylation are keto acid 21 from 2 -hydroxyl at ion and hydroxy acid 21 from 5 -hydroxylation. Trace amounts of 7 y 21> H ve also been detected as urinary metabolites (34). The interrelationships of these metabolites as shown in Figure 2 have been confirmed by administration of each metabolite to F-344 rats (37). The other metabolites which are routinely observed in the urine are NNN-1-N-oxide U1 and 5-(3-pyridyl)-2-pyrrolidinone [norcotinine, ]. The p-hydroxy derivatives 2. 1 were also detected in the urine of NNN treated rats, but at less than 0.1% of the dose (36). An HPLC trace of the urinary metabolites of NNN is shown in Figure 3. Urine is the major route of excretion (80-90% of the dose) of NNN and its metabolites in the F-344 rat in contrast to NPYR which appears primarily as CO2 (70%) after a dose of 16 mg/kg (17). This is because the major urinary metabolite of NNN, hydroxy acid 21> fs not metabolized further, in contrast to 4-hy-droxybutyric acid [2, Figure 1] which is converted to CO2. In addition, a significant portion of NNN is excreted as NNN-l-N-oxide U ], a pathway not open to NPYR. 

Figure 5-4. Metabolic activities of major organs in the fed state. The relative activities of major metabolic pathways or processes in each of the organs are indicated by their font sizes. The exchange of nutrient materials and fuel molecules through the bloodstream illustrates the interrelationships of these organs. In the absorptive condition, all organs share the bounty of nutrients made available by digestion of food by the intestine. PPP, pentose phosphate pathway FA, fatty acids TAG, triacyl-glycerol.

As as been pointed out in Boxes 3-C and 17-C, the use of 13C and other isotopic tracers together with NMR and mass spectroscopy have provided powerful tools for understanding the complex interrelationships among the various interlocking pathways of metabolism. In Box 17-C the application of 13C NMR to the... 

Fig. 1. Some interrelationships between glucose-6-phosphatase and other enzymes of carbohydrate metabolism [from Nordlie (10) copyright (1968), Academic Press, Inc. Reproduced by permission]. Numbers in parentheses indicate the relative disposition per 100 molecules of glucose phosphorylated of glucose-6-P via four alternate metabolic pathways, according to Ashmore et al. (69). Further details are given in the text.

In addition to being incorporated into tissue proteins, amino acids, after losing their nitrogen atoms by deamination and/or transamination, may be catabolized to yield energy or to form glucose. Conversely, the nonessential amino acids may be synthesized from carbohydrate metabolism intermediates and ammonia or from essential amino acids. This section is devoted to the mechanisms of such metabolic processes and their interrelationships with carbohydrate and lipid metabolic pathways. 

Figure 20.15 Interrelationships between the serine and glycine metabolic pathways. FH4-"C" indicates 5,10-methylenetetrahydrofolate. (Adapted from Yoshida T, Kikuchi G. Comparative study on major pathways of glycine and serine catabolism in vertebrate livers. ) Biochem 72 1503-1516, 1972.)...

Carman, G.M., and Henry, S.A., 1999, Phospholipid biosynthesis in the yeast Saccharomyces cerevisiae and interrelationship with other metabolic processes. Prog. Lipid Res. 38 361-399. Chang, H.J., 2001, Role of the unfolded protein response pathway in phospholipid biosynthesis and membrane trafficking in Saccharomyces cerevisiae. Department of Biological Sciences, Carnegie Mellon University. 

Although the complexities involved in the interrelationships of various metabolic pathways within the intact cell have made it difficult to evaluate the role of... 

In support of these investigations, a well-structured yet flexible data model is required. Metabolic pathways are a way of describing molecular entities and their interrelationships. From a data management point of view, a container for chemical structures has to be established that meets several requirements ... 

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