The Intracellular Distribution of Adenosine Triphosphate
Eukaryotic cells are not internally homogeneous, but are compartmentalized into cytoplasmic and nuclear ground substances and the numerous organelles embedded therein. Because of spatial heterogeneity, a comprehensive understanding of the cell's metabolism requires not only data on the rates of synthesis and utilization of adenosine triphosphate, but also a description of how ATP is distributed. Unfortunately, it is difficult to measure ATP concentrations regionally within cells, so that very little is known about its distribution. When considering its role in specific metabolic pathways, it is usual to accept ATP concentrations averaged over the entire cell (or tissue) volume as an adequate measure of local concentrations. This is equivalent to assuming that intracellular ATP is uniformly distributed. (Mitochondria, thought to have much lower ATP levels than the surrounding cytoplasm, are usually exempted from this assumption.) With the development of cryomicrodissection (Frank and Horowitz, 1978; Tluczek et al., 1984), it is now possible to measure ATP in regions of a single cell, the amphibian oocyte. We are beginning to develop some notion as to the assumption's validity and, when necessary, the reasons for its failure.
KeywordsNuclear Envelope Nuclear Concentration Diffusional Equilibrium Control Oocyte Cytoplasmic Concentration
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