Label incorporation

FIGURE 31 -10 Cerebral amino acids and carbohydrates incorporate 13C label from infused glucose. The top panel shows a 13C NMR spectrum obtained from a gray-matter-rich volume in the human head. (From reference [141].) The right panel shows label incorporation into brain glycogen and glucose in humans. (From reference [142].) The stack plot illustrates the rate of label incorporation into many compounds and carbons in the rat brain. (From reference [ 143].) In all studies, glucose labeled at the 1 or 6 position was administered intravenously. 

Thus, 2-methylthio-4,6,7-triphenylpteridine is a mM reactive compound. It shows activity to nucleophiles at four ring carbon atoms at C-4 [Sn(AN-RORC)], at C-2 [Sn(AE)], and at C-6, as well as at C-7 (purine formation). Based on qualitative product studies and N-label incorporation studies, the order of reactivity is approximately C-4 > C-2 > C-7 > C-6. 

Pool-Loading Experiments and Possibility that Reduction in Incorporation Reduces Influx into Soluble Pool. In order to empirically eliminate the possibility that the observed reduction in uptake of labelled amino acids into the soluble pool was an indirect result of an inhibition of incorporation, it was necessary to experimentally separate the influx and incorporation systems in vivo. The operational compromise required to accomplish this has been given by Sacher (55), and involves in the present case measuring the rates of label incorporation in control and treated tissues which have had their soluble pools fully loaded with unlabelled amino acid. Thus, the label-specific... 

Table IV shows typical results of the pool overloading experiments in the soybean trifoliate leaf. Visible damage to ozonated plants after 24 hr incubation was, as usual, taken as necessary for an experiment to be valid. Clearly, incorporation of label into protein was reduced where casein hydrolysate had been used in control and treated discs to overload the soluble pools. Just as clearly, total counts present in the soluble pool of treated tissue were reduced by ozonation whatever the after-treatment. The reduction of label in the soluble pool in control and ozonated discs due to casein treatment was approximately 30% in each case the reduction of label incorporation due to ozone was about 36% in the case of water treatment and about 14% in the case of casein treatment.

When the reaction is run in the presence of 13CO and stopped after one half-life, not only is the label incorporation into recovered starting material negligible, as predicted by the mechanism, but the label incorporation into H2Os2(CO)s exceeds that required by the mechanism. This shows that it is undergoing carbonyl exchange under the reaction conditions and suggests that such dinuclear species are much more labile than their mononuclear counterparts. 

Another application of LC-NMR in natural products chemistry concerns biosynthetic studies employing feeding experiments with stable isotope-labelled compounds. H NMR spectra allow the determination of the amount of isotopic label incorporated into metabolites, e.g. by observing signals that arise from /-couplings of protons to 13C-labelled nuclei [41,42],... 

Radioisotope labeling Incorporation of a radioactive label into a compound Characterization of biomolecular components tracing reaction pathways... 

These results could be explained if, as was suggested by the data of Dillwith et al. (14). there is a pathway In which propionate is directly converted to acetate with the loss of carbon 1 and the oxidation of carbon 3. With a pathway of this type, propionate labeled in carbon 1 would lose its label if it were converted to acetate prior to incorporation into other compounds. However, if propionate were labeled in carbon 2 or carbon 3 it would retain its label upon conversion to acetate. Therefore, any label incorporated into JH or hydrocarbon from propionate labeled in carbon 1 would have to be the result of propionate being utilized as an intact unit. Incorporated label from propionate labeled in carbon 2 or carbon 3 could result from direct Incorporation of propionate or from conversion of propionate to acetate prior to being utilized for JH or hydrocarbon biosynthesis. Thus, the labeling patterns seen by Schooley, ejt al. (O and Dillwith, et a l. (14) could be the result of the retention of label from carbon 2 or carbon 3 of propionate, and the loss of label from carbon 1 of propionate during the conversion of propionate to acetate. 

Butterfield DA, Drake J, Pocemich C, Castegna A (2001) Evidence of oxidative damage in Alzheimer s disease brain central role for amyloid beta-peptide. Trends Mol Med 7 548-554 Butterfield DA, Hensley K, Htirris M, Mattson M, Carney J (1994) beta-Amyloid peptide free radical fragments initiate synaptosomal Upoperoxidation in a sequence-specific fashion impUcations to Alzheimer s disease. Biochem Biophys Res Commun 2(X) 710-715 Butterfield DA, Hensley K, Cole P, Subramaniam R, Aksenov M, Aksenova M, Bummer PM, Haley BE, Carney JM (1997) Oxidatively-induced structural alteration of glutamine synthetase assessed by analysis of spin labeled incorporation kinetics relevance to Alzheimer s disease. J Neurochem 68 2451-2457... 

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