Pathways of glucose utilization and ribose synthesis in the chick embryo Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/2z10wt686

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  • The production of C¹⁴O₂ metabolized from glucose labeled in specific carbon atoms by homogenates of chick embryonic and adult heart was compared by the radiorespirometric technique. Homogenates of early (two to five days of incubation) embryo hearts were found to utilize the phosphogluconate pathway of glucose catabolism to a greater extent, relative to the glycolytic-Krebs cycle pathway, than did homogenates of hearts from older embryos or adult chicks. This observation was supported by results with t-gluconolactone-1-C¹⁴, which was metabolized to C¹⁴O₂ to a greater extent than glucose-U-C¹⁴ by early chick embryo heart. Further, the stimulation of the oxidation of glucose-1-C¹⁴ to C¹⁴O₂ by added triphosphopyridine nucleotide was much greater in the early embryo heart than in older embryo or adult heart. Chick embryos of the 11 to 13 somite stage were explanted for one to two days onto a medium containing glucose-1, -2, or -6-C¹⁴, acetate-1-C¹⁴, pyruvate-1-C¹⁴, ribose-1 or ribose-U-C¹⁴ The major chemical fractions, as well as the degradation products of ribonucleic acid and deoxyribonucleic acid, were examined for radioactivity. Distinct differences in the embryo area and the membrane area were found in the utilization of the labeled substrates. The membrane area incorporated labeled glucose first, followed by a transfer to the embryo area. Collection of C¹⁴O₂ at intervals from explants administered glucose-1, -2, or -6-C¹⁴ indicated a small contribution to oxidative metabolism by the phosphogluconate route. A drop in interval recovery of C¹⁴O₂ after 24 hours of explantation was not reflected by a plateau in incorporation of C¹⁴ into the chick embryo, and was interpreted as a reduction in the oxidative and an increase in the non-oxidative metabolism of glucose at this time. The distribution of C¹⁴ in ribose of the chick embryo demonstrated that the non-oxidative pathway for its formation predominated in the explants. The relative contribution of non-oxidative pathways for ribose synthesis was estimated to be between 50 and 75 percent for embryos explanted for 24 hours, and 80 to 90 percent for 48-hour explants. About 10 percent of the label in ribose was estimated to have been derived from glucose carbon after conversion to non-pentose cycle or non-glycolytic pathway intermediates. Labeling of deoxyribonucleic acid, as well as the purines and deoxyribose moieties, exceeded that of the ribonucleic acid and the corresponding breakdown products, when glucose, acetate-1-C¹⁴, or pyruvate-1-C¹⁴ were the substrates but was less than that of ribonucleic acid and its constituents when ribose-1-C¹⁴ or ribose-U-C¹⁴ were the substrates. The labeling of purines and pyrimidines of ribonucleic acid and of purines of deoxyribonucleic acid suggested that C¹⁴O₂ fixation was an important factor in their formation. The possibility of separate pools of ribonucleic acid and deoxyribonucleic acid precursors was suggested by their relative labeling from the C¹⁴ substrates. It is suggested that the deoxyribose of deoxyribonucleic acid was formed in part by reactions other than the direct reduction of ribose.
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