Metabolic organization in neurospora
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Several mechanisms of metabolite channeling have been discovered in arginine and pyrimidine biosynthesis in Neurospora. In the case of carbamyl phosphate, a pyrimidine specific "pool" of this compound is actually bound to a nucleolar enzyme aggregate which both makes and uses this compound. In the arginine pathway, another pool of carbamylphosphate appears to be made and used in mitochondria, to which the pool is confined. Finally, the large pools of arginine and ornithine found in Neurospora appear to be storage pools which are not on the main line of anabolic reactions . These pools also remain untouched by the catabolic enzymes, arginase and ornithine transaminase, because the enzymes are in the cytoplasm and the pools are sequestered in a membrane-bound vesicle. All of these "spatial" channeling mechanisms coexist with the more familiar, "kinetic'' regulatory mechanisms, such as feedback inhibition and repression. The integration of spatial and kinetic regulatory phenomena in the cases discussed represents a fundamental and often overlooked aspect of metabolic organization in eucaryotes .