Intracellular compartmentation and transport of metabolites.

The intracellular locations of enzymes and metabolites were determined for ornithine metabolism in Neurospora. Pulse label experiments were used to measure the rates of intracellular translocations and the sizes of compartmented pools of metabolites in the mitochondrial, cytosolic and vesicular compartments. The results indicate that rapid equilibration occurs between these pools during growth in minimal medium, although the vast majority of the ornithine is confined to the vesicular compartment. Arginine, the biosynthetic end-product of ornithine metabolism, regulates ornithine utilization through a combination of feedback inhibition, repression, and control of intracellular translocations. The last phenomenon plays a decisive role indicating that the regulation of intercompartmental translocations may be a common mechanism in rapid adaptation responses in eukaryotic cells.