Article

Some Aspects of Urea and Pyrimidine Metabolism during Development

Biologia neonatorum. Neo-natal studies 01/1965; 9(1):187-96. DOI: 10.1159/000239989
Source: PubMed
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    ABSTRACT: Extract: Activities of two enzymes of the de novo pyrimidinc biosynthetic pathway, aspartate transcarbamylase and dihydro-orotase, and one enzyme of the salvage pathway, uridine kinase, were assayed in the liver, heart, brain, and intestine during embryogensesis of the chick, to assess the relatio of these pathways to celluar proliferation and organ growth. As the period of embryogenesis ended, the increment of cellular prolifertation, as determined by changes in amount of DNA, of liver, brain, and heart decreased, while that of intestine remained relatively constant. The most elevated activities for both enzymes of the de novo pathway were observed in the earliest stages of development, decreasing thereafter with age. These two enzymatic activities changed sychronously in each of the tissues studied. In each organ, the highest activities of the de novo pyrimidine biosynthetic enzymatic patterns during development paralleled the overall growth rates of different organs. The activity of uriding kinase increased throughout embryonic development in the organs investigated, in contrast to the activities of the enzymes of the pathway of de novo Pyrimidine biosynthesis.
    Preview · Article · Feb 1970 · Pediatric Research
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    ABSTRACT: In vitro incorporation of [14C] bicarbonate into orotic acid by rat liver slices was used to study the rate of orotic acid (OA) biosynthesis in the presence of physiological (0.73 mM) and saturation concentrations (5 mM) of NH4Cl. The influence of body size on OA synthesis in rats fed purified L-amino acid diets with (C) or without (-Arg) was examined. OA biosynthesis was significantly greater at both NH4Cl concentrations examined in liver slices obtained from -Arg rats for all sizes of rats. A linear decrease (r = 0.92) in OA synthesis as a function of body size was observed for rats fed either of the diets. The rate of OA biosynthesis was also found to increase linearly (r = 0.98) in livers from rats fed increasing dietary protein when determined by incubation with physiological concentrations of NH4Cl. OA biosynthesis was also found to increase with increase in length of fasting. Alteration in urinary OA and urea confirm these rates of synthesis. These results support the hypothesis that when the urea cycle is overtaxed, carbamyl phosphate (CP) synthesized intramitochondrially by CP synthetase I may be shunted into pyrimidine biosynthesis.
    Preview · Article · Dec 1979 · Journal of Nutrition
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    ABSTRACT: The developmental changes of glutamate dehydrogenase activity in the fetal and neonatal rat liver were investigated, as well as the effects of branched-chain amino acids on this enzyme. Hepatic glutamate dehydrogenase activity showed a marked increase at the end of the fetal period and peaked on the 5th day of neonate at approximately 3 times higher than the adult level. Glutamate dehydrogenase was activated by leucine, isoleucine, and valine in this order when they were added to isolated intact liver mitochondria in vitro. The enhancement of enzyme activity was more marked in fetal rats than in adults. In contrast, when branched-chain amino acids were added after disrupting the mitochondrial membrane by sonication, only leucine slightly activated glutamate dehydrogenase, while isoleucine and valine slightly inhibited its activity. Our findings suggest that glutamate may be actively synthesized in the developing rat liver mitochondria and then transaminated to other nonessential amino acids for protein synthesis, and that increased intramitochondrial branched-chain amino acid concentrations may enhance glutamate dehydrogenase activity. This anabolic metabolism will contribute to the fetal growth and development.
    No preview · Article · Feb 1992 · Biology of the Neonate