Purines: supply by liver to tissues.
01 Nov 1970-American Journal of Physiology (American Physiological Society)-Vol. 219, Iss: 5, pp 1263-1267
About: This article is published in American Journal of Physiology.The article was published on 1970-11-01. It has received 74 citations till now.
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TL;DR: Succinyladenosine and succinylaminoimidazole carboxamide riboside were found in body fluids from 3 children, including a brother and sister, with severe psychomotor delay and autism.
288 citations
TL;DR: De novo synthesis of adenine nucleotides increased almost 100% in the heart in situ and in the isolated perfused heart during the first hour of recovery from asphyxia or ischemia, and this acceleration is regarded as an adaptive process contributing to the postanoxic restoration of normal adenines nucleotide levels.
Abstract: De novo synthesis of adenine nucleotides was measured in rat hearts in situ and in isolated perfused rat hearts under normal conditions and during recovery from asphyxia or ischemia. Using l- 14 C-glycine as the precursor substrate, rates of de novo synthesis were determined from the total radioactivity of adenine nucleotides and from the mean specific activity of intracellular glycine. The rate of de novo synthesis of adenine nucleotides was 8.4±1.42 nmoles/g hour -1 in the heart in situ and 1.3±0.12 nmoles/g hour -1 in the isolated perfused heart. De novo synthesis of adenine nucleotides increased almost 100% in the heart in situ and about 580% in the isolated perfused heart during the first hour of recovery from asphyxia or ischemia. This acceleration is regarded as an adaptive process contributing to the postanoxic restoration of normal adenine nucleotide levels. Possible biochemical mechanisms that might be involved in the stimulation of the de novo pathway are a release of feedback inhibition of 5-phosphoribosyl-1-pyrophosphate amidotransferase, an enhanced synthesis of 5-phosphoribosyl-1-pyrophosphate, and an alternate way of 5-phosphoribosyl-amine formation.
193 citations
TL;DR: The chapter discusses the some general principles about transport processes in animal cells, and examines the evidence for specific transport systems for bases and nucleosides, attempting to differentiate between membrane and metabolic events.
Abstract: Publisher Summary This chapter discusses the membrane transport of purine and pyrimidine bases and nucleosides in animal cells. In general, these compounds enter animal cells by facilitated diffusion, and transport carriers are clearly separate from the enzymes responsible for subsequent intracellular metabolism. The carriers are proteins which have lateral mobility in the plane of the membrane. The chapter discusses the some general principles about transport processes in animal cells, and then examine: (1) the evidence for specific transport systems for bases and nucleosides, attempting to differentiate between membrane and metabolic events; (2) the detailed characteristics of the systems, with particular attention to implications for carrier structure based on substrate specificity and sensitivity to inhibition by chemical agents; (3) the physiological control of transport; and the evidence that carriers are mobile components of biological membranes and as such may be functionally modified by interactions with other membrane components. Substances that inhibit transport in cells depend on exogenous purines for nucleic acid synthesis may impose selective growth control. Malignancies of bone marrow (leukemia) and of the gastrointestinal tract could fall within this category; such inhibitors should not damage the majority of cells and tissues that have the capacity to synthesize purines de novo. In addition, since carrier properties such as susceptibility to inhibition are highly variable among cells, inhibitors that are particularly effective against specific cell types may be developed.
134 citations
TL;DR: The consequences of changes in substrate concentration, in temperature, and in the effective kinetic parameters of transport and phosphorylation on rates of uptake demonstrate the complexity of this interdependence and the errors of interpretation that can accrue if the complexity is overlooked.
Abstract: Publisher Summary Three main classes of nutrients—nucleosides, nucleobases, and hexoses (and possibly a fourth, the water-soluble vitamins)—are taken up into cultured cells as a result of the tandem action of a nonconcentrative transport system and an intracellular enzyme that introduces into the transported substrate an anionic group thus confering impermeability. For several substrates representing the first three of these nutrient classes, both members of the uptake pathway are characterized kinetically: (1) the transport systems with cells and substrates that, by virtue of enzyme deficiency, adenosine triphosphate (ATP) depletion, or chemical design, are metabolically inert and (2) the enzymes, as purified proteins, in idealized milieu. The consequences of changes in substrate concentration, in temperature, and in the effective kinetic parameters of transport and phosphorylation on rates of uptake demonstrate the complexity of this interdependence and the errors of interpretation that can accrue if the complexity is overlooked. Flux in a tandem pathway follows a biphasic time course. The first phase corresponds to the attainment of steady-state levels of free intracellular substrate. The second phase represents steady-state flux through the pathway—that is, the rate of accumulation of impermeable product.
118 citations
TL;DR: Hydlysis of endogenous AMP was studied in the perfused heart and the maximum activity of 5'-nucleotidase in perfused hearts is equal to or greater than that found in heart homogenates; thus, all of the enzyme is accessible to AMP added externally.
116 citations