Graduate Thesis Or Dissertation
 

Kinetics of synthesis and degradation of chicken liver xanthine dehydrogenase

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  • The role of synthesis and degradation in controlling enzyme concentrations was studied. Concentrations of chloride and arginine were determined for blood and liver at various stages of development from the embryo to the 8 day old chicken. The chloride concentrations were used to obtain the volume of extracellular blood in the liver. Using these values together with the data for total arginine, it was possible to calculate the intracellular and extracellular arginine concentrations in the liver. Extracellular arginine represented. 19%, 15% and 26% of the total arginine in the 14 day embryo, 1 day old. chick and 8 day old chick respectively. The kinetics of incorporation of L-(guanido- 14 C)-arginine and. L-valine- 14 C(u) into the blood amino acid pool and intracellular liver amino acid pool of the chick during various stages of development were measured. Intravenous injection of isotopic amino acid leads to results similar to a pulse labeling pattern, since more than 80% of the tracer is consumed after 60 minutes. The time-integrated radioactive amino acid pools were determined for each age of chick. Thirty minutes after injection of radioactive arginine or valine, 40% of the radioactivity remaining in the amino acid pools is found in compounds other than arginine or valine. These results are indicative of probable matabolism of these amino acids into other compounds. Xanthine dehydrogenase concentrations and the wet weight of liver also were measured during development. The liver wet weight increases most rapidly in the embryo. The enzyme activity is low in the embryo, rises rapidly upon hatching and reaches a high level by the eighth day after hatch. The rate constants of synthesis and degradation were determined for xanthine dehydrogenase during chick liver development, by purifying the labeled enzyme and measuring the rate of incorporation of label from arginine or valine into the protein. The rate constants for synthesis using L-(guanido- 14 C)-arginine are 3.7 x 10- 12 2.8 x 10 12 and. 0.8x 10-12 moles XDH per minute per gram of liver for the 8 day chick, 1 day chick and 14 day embryo respectively. The t l/2 values for the 8 day chick, 1 day chick and 14 day embryo are 17, [infinity], and [infinity] hours respectively. When L-valine- 14 C(u) is used as substrate, the rate constant for synthesis is 7. 0 x 10-12 moles XDH per minute per gram of liver for the 1 day chick. The rate of synthesis of XDH relative to the rate of synthesis of total soluble protein for the 1 day chick is 1. 7 for valine as substrate and. 0. 9 for argiriine. The role of synthesis and degradation in determining enzyme concentrations is discussed. Also included. is a critique of the methodology.
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file details Epstein_Arnold_1971.pdf 2017-08-14 Öffentlich Herunterladen