Comparison of the uracil catabolic activity of liver cell suspensions and slices

S T JACOB & P M BHARGAVA

Regional Research Laboratory, Hyderabad India

Published in: Biochemica et Biophysica Acta, 1964, 91, 650-652.

Abstract:

Several workers have demonstrated that [14C]uracil can be incorporated into the various tissues of adult rats, both in vivo and in vitro, though in considerably smaller quantity than pyrimidine nucleosides of orotic acid1- 4 . CANELLAKIS2 suggested that the high rate of replacement of RNA-uridylic acid by orotic acid as compared to uracil, at low substrate concentrations, may be due to the following three reasons: (a) the low concentration of free orotic acid in the tissue5 and consequently, little dilution of the added precursor by endogenous orotic acid; he observed that at high concentrations (6 μmoles/ml) at which the dilution of the exogenously added precursor by the endogenous pool may be small, even uracil, which has been considered not to be a precursor of RNA-uridylic acid, is incorporated to an extent which compares favourably with that of uridine and orotic acid. (b) The lower capacity of the liver to degrade orotic acid when compared to uracil;liver slices; were found to degrade 90-98 % of the administerrd [2-14C]uracil to 14CO2 in 1.5 h when the uracil concentration was o.1-0-4 μmole/ml, while at these concentrations [2- 14C] orotic acid was degraded to an extent of only 12- 20 %; at a higher concentration (6 μmoles/ml), at which uracil was incorporated into RNA to a significant extent, the degradation was only 22 %. (c) The possible inability of the UMP formed from orotic acid to equilibrate with the tissue pool of UMP.

We recently observed4 that hepatic cells obtained in suspension by a recently described method6 incorporate significantly more [14C]uracil into their RNA than do liver tissue slices. It was, therefore, considered desirable to determine if this enhanced incorporation was related to one of the reasons advanced by CANELLAKIS for the low incorporation of uracil in liver slices.

PMID: 14262455| DOI: 10.1016/0926-6550(64)90017-9

Keywords:
Carbon Dioxide, Carbon Isotopes, Carcinoma, Hepatocellular, Liver/cytology, Metabolism, Orotic Acid
Perfusion, RNA

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Comparison of the uracil catabolic activity of liver cell suspensions and slices. S T JACOB & P M BHARGAVA. Biochemica et Biophysica Acta, 1964, 91, 650-652.

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