Endogenous pools

Production of poly(3HB-co-3HV) co-polymer in plants has recently been demonstrated by the PHA group of Monsanto [27], which acquired the PHA business of Zeneca in 1996. In the commercial production of poly(3HB-co-3HV) from R. eutropha, propionate is added to the growth media in order to create an intracellular pool of propionyl-CoA which can be condensed to acetyl-CoA to form 3-ketovaleryl-CoA. The 3-ketovaleryl-CoA is then reduced by the aceto-acetyl-CoA reductase to give 3-hydroxyvaleryl-CoA, which is co-polymerized with 3-hydroxybutyryl-CoA to synthesize poly(3HB-co-3HV) (Fig. 1). For the synthesis of poly(3HB-co-3HV) in plants, it was thus necessary to create an endogenous pool of propionyl-CoA which could be used by the PHA pathway. 

Chang CJ, Nolan EM, Jaworski J et al (2004) Bright fluorescent chemosensor platforms for imaging endogenous pools of neuronal zinc. Chem Biol 11 203-210... 

This suggests that the unconjugated urinary cholesterol may reflect an endogenous pool. 

The stationary phase and aminopterin method suffers from the disadvantage that it takes a week to prepare the cells but thereafter it is straightforward and DNA synthesis can be followed without interference from endogenous pools ( 12.1.1). 

On the other hand, the increased GPx activity (possibly via protein synthesis) might be associated with an oxidative stress induced by DHA (22 6, -3) estoified to tri ycerides is rapidly redistributed within blood lipxqnioteins. The DHA (22 6, w-6) bound and circulate with the albumin fraction not only inhibit platelet aggregation but also influences its uptake into phospholipid species by target tissues (98). DHA therefore seems to impact platelet fatty acid metabolism through unique and novel mechanisms. 

It should be noted that the labelled precursor is normally highly diluted by the endogenous pool of unlabelled acetate and so no coupling is ob-... 

It should be noted that the labelled precursor is normally highly diluted by the endogenous pool of unlabelled acetate and so no 13C-13C coupling is observed between pairs of atoms derived from different acetate units. In some cases such extra inter-acetate couplings may be observed and in a few exceptional cases where little or no dilution by endogenous acetate occurs, the further 13C-13C couplings which result can make interpretation of the spectra problematic. This problem can usually be overcome by the simple expedient of diluting the labelled precursor 2 - 3-fold with unlabelled material prior to incorporation... 

FIGURE 6.12 Urine NT x low and high endogenous pools data over a time span of 21 months. Upper panel high pool. Lower panel low pool. Vertical arrows kit lot changes. 

The possibUity of multiple pathways in bile acid biosynthesis in man has been discussed by Vlahcevic et al. [180-182]. A number of labelled 7 -hydroxylated intermediates in bile acid biosynthesis were administered to bile fistula patients as well as patients with an intact enterohepatic circulation. In accordance with previous work with bile fistula rats, the spedfic activity of the isolated chohc add was in general considerably lower than that of chenodeoxychohc acid. On the basis of this finding, it was suggested that a portion of chohc acid was synthesized via a route not involving initial 7a-hydroxylation of cholesterol. It must then be assumed that the administered intermediate mixes with the endogenous pool of the same steroid. However, due to compartmentation, the metabolic fate of a precursor reaching the hepatocyte might be different from that of the the same compound formed within the cell. Normally, the different precursors are present in the cells in trace amounts... 

The data provided by Dugrillon and Gartner are more impressive reasonable potency, evidence (though limited) of structural specificity and selectivity for the EGF signaling pathway. However, the evidence that 6-iodolactone is a mediator of iodide is restricted to one particular parameter, the inhibition of EGF proliferative action, and a conclusive demonstration that it can be formed in sufficient amounts from the endogeneous pool of arachidonic acid remains to be provided. 

N-(2-hydroxyethyl)-nicotinamide, which undergoes further side-chain degradation to nicotinuric acid and, subsequently, nicotinamide and nicotinamide metabolites (e.g., nicotinic acid and N-methylnicotinamide). The nicotinamide derived from nicorandil merges into the endogenous pool of nicotinamide adenine dinucleoside coenzymes. Its elimination half-life is approximately 1 hour. Approximately 30% of nicorandil is excreted into the urine as metabolites, with less than 1% excreted unchanged. 

In fact, H-24-methylenecholesterol has been traced unchanged through two generations of bees (28). Thus, there is a very unusual mechanism that enables the workerTee to selectively transfer certain dietary sterols or sterols cycled from their endogenous pools to the brood food to maintain a constant supply of certain sterols for the brood food. The utilization of neutral sterols by the honey bee and the inability to produce cholesterol from the dealkylation of 24-alkyl C20 and C29 phytosterols is reflected in the recent isolation of makisterone A as the major ecdysteroid at peak titer in the honey bee pupa (29). 

Asymmetric labeling of sesquiterpenes by labeled mevalonic acid or other precursors, presumably caused by an endogenous pool of DMAPP, has been reported for a few sesquiterpenes. Label primarily is introduced into the portions of the molecules derived from IPP (Charlwood and Banth-orpe, 1978). 

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