Metabolic pool

Nitrogen is normally supplied as an ammonium compound in dtric acid fermentations and suffident has to be supplied to enable the effect of manganese deficiency (increased levels of ammonium in the metabolic pool) to occur. Remember that increased metabolic pool ammonium has the effect of releasing the allosteric controls exerted on phosphofructokinase. 

Figure 11.1. A flow-model scheme for treating the protein routing question. Labels refer to flow rates of carbon. The total carbon flux, into and out of the body, is 1, divided into F (for protein) and 1 - F for the remainder. The significant relevant internal fluxes are between the amino acid pool (coupled to the body protein pool), and the energy metabolism pool . The extent to which protein routing is observable in the body protein composition depends on the value ofX (See Fig. 11.2). Numbers in refer to suggested isotopic fractionations associated with a metabolic path, which are consistent with the data of the Ambrose and Norr (1993) and Tieszen and Fagre (1993) data set (see Section 4.1).

Manufacturing processes for cephalosporin C and benzylpenicilhn are broadly similar. In common with mai other antibiotic fermentations, no specific precursor feed is necessary for cephalosporin C. There is sufficient acetyl group substrate for the terminal acetyltransferase reaction available fiom the organism s metabolic pool. 

For example, initially MBP and PLP exhibit half-lives of 2-3 weeks, but later their half-lives are too long to be calculated accurately. A possible interpretation of these data is that some of the newly formed myelin remains in outer layers or near cytoplasmic pockets (incisures and lateral loops) where it is accessible for catabolism - thus accounting for the rapidly turning-over pool. The more stable metabolic pool would consist of deeper layers of myelin less accessible for metabolic turnover. 

Nickel is considered essential to animals because it is present in the fetus or newborn, is homeostatically regulated, the metabolic pool of nickel is specifically influenced by hormonal substances or pathologic processes, certain metalloproteins contain nickel, and because nickel deficiency has been induced experimentally in certain species of birds and animals (NAS 1975 USPHS 1977 Kirchgessner and Schnegg 1980). In general, the nickel deficiency syndrome can be cured or prevented by trace amounts of nickel (NAS 1975). However, nickel administration may not be successful in reversing all abnormalities produced by nickel deprivation (USPHS 1977). 

The metabolism of cyanide has been studied in animals. The proposed metabolic pathways shown in Figure 2-3 are (1) the major pathway, conversion to thiocyanate by either rhodanese or 3-mercapto-pyruvate sulfur transferase (2) conversion to 2-aminothiazoline-4-carboxylic acid (Wood and Cooley 1956) (3) incorporation into a 1-carbon metabolic pool (Boxer and Richards 1952) or (4) combining with hydroxocobalamin to form cyanocobalamin (vitamin B12) (Ansell and Lewis 1970). Thiocyanate has been shown to account for 60-80% of an administered cyanide dose (Blakley and Coop 1949 Wood and Cooley 1956) while 2-aminothiazoline-4-carboxylic acid accounts for about 15% of the dose (Wood and Cooley 1956). The conversion of cyanide to thiocyanate was first demonstrated in 1894. Conversion of cyanide to thiocyanate is enhanced when cyanide poisoning is treated by intravenous administration of a sulfur donor (Smith 1996 Way 1984). The sulfur donor must have a sulfane sulfur, a sulfur bonded to another sulfur (e.g., sodium thiosulfate). During conversion by rhodanese, a sulfur atom is transferred from the donor to the enzyme, forming a persulfide intermediate. The persulfide sulfur is then transferred... 

Many reports on the effects of ozone and PAN on physiologic processes (net photosynthesis, stomatal response, and water relations) and on metallic activity (including in vivo and in vitro studies of individual enzymes, enzyme systems, metabolic pathways, metabolic pool relationships, cell organelles, and plant tissue studies) have appeared since 1964. 

Diagram showing the addition of radiotracer A at t = 0 (termed the "pulse") and the subsequent addition of excess unlabeled A (termed the "chase"). The relative size of the lettering serves to indicate the time-course of radiolabeled entry and exit from each metabolic pool. 

The effects of ozone are not limited to altering metabolic pools in plant foliage they can also induce the formation of toxic compounds. Leachate was collected from fescue leaves 2 weeks following a 2 hr exposure to 590 yg/m ozone and used to irrigate clover plants (20). Top and root dry weights of ladino clover were unaffected by leachate from ozone-treated fescue leaves. However, the leachate from the ozone-exposed fescue leaves reduced the nodule number of ladino clover (Table IV). 

The lipases of milk are apparently inactive in the udder and at the time of milking. Milk always contains relatively large proportions of unesterified fatty acids (Thomas et al. 1955A), but these may be left over from the metabolic pool. 

Three Hexose Phosphates Constitute the First Metabolic Pool... 

The Conversion of Triose Phosphates to Phosphoglycerates Occurs in Two Steps The Three-Carbon Phosphorylated Acids Constitute a Third Metabolic Pool... 

Except for glycerate-l,3-bisphosphate all of the intermediates in the pathway are pictured as belonging to one of three metabolic pools. Within each metabolic pool the intermediates are readily interconvertible and usually present in relative concentrations close to their equilibrium values. Between the pools the concentrations of the intermediates can be very different because of the lack of rapid intercon-... 

Fructose-1,6-bisphosphate and the Two Triose Phosphates Constitute the Second Metabolic Pool in Glycolysis... 

The metabolic pool that consists of fructose-1,6-bisphosphate and the two triose phosphates—glyceralde-hyde-3-phosphate and dihydroxyacetone phosphate (DHAP)—is somewhat different from the other two pools of intermediates in glycolysis because of the nature of the chemical relationships between these compounds. In the other pools the relative concentrations of the component compounds at equilibrium are independent of the absolute concentrations. Because of the cleavage of one substrate into two products, the relative concentrations of fructose-1,6-bisphosphate and the triose phosphates are functions of the actual concentrations. For such reactions, the relative concentrations of the split products must increase with dilution. (For the reaction A v B + C, the equilibrium constant is equal to [B][C]/[A], If the concentration of A decreases, for example, by a factor of 4, equilibrium is... 

Glycerate-3-phosphate, glycerate-2-phosphate, and phos-phoenolpyruvate (PEP) make up another equilibrium group of metabolites that, like the hexose phosphates or the triose phosphates, function as a single metabolic pool (see fig. 12.13). 

The glycolytic pathway resembles a series of lakes (metabolic pools) connected by short rivers (the reactions between the pools). This pattern is reflected in the ways that functional metabolic relationships have evolved. Reactions involving ATP and ADP occur in the interconnecting reactions, or rivers. Clearly this is where they are expected, because an ATP-linked reaction within a metabolic pool makes no more sense than a hydroelectric power plant in the middle of a lake. 

Relationships in glycolysis and gluconeogenesis. Points at which ATP is produced or consumed are indicated. Compounds in the same metabolic pools are indicated by purple boxes. Three small pseudocycles (la, II, III) in the paired sequences occur between glycogen and pyruvate, or between glycogen and glucose (lb, II, III). Only enzymes that are unique to either glycolysis or gluconeogenesis are indicated (screened in blue). 

The organization of glycolysis and gluconeogenesis as a series of connected metabolic pools makes it possible for most of the same enzymes to function in both directions. Only the reactions connecting the metabolic pools require different enzymes and a coupling to the ATP-ADP system to make them thermodynamically feasible in the direction of gluconeogenesis. 

Aconitase, the enzyme that catalyzes this isomerization, is named for the fact that the unsaturated compound formed by removing H20 from either citrate or isocitrate, cA-aconitate, can also serve as substrate or product. Aconitase catalyzes the attainment of equilibrium between citrate, isocitrate, and civ-acon itate. The three compounds may be considered as belonging to the same metabolic pool. 

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