title: Arginine catabolism in Neurospora: cycling of ornithine.
abstract: We measured the metabolism of ornithine in Neurospora during the transition from minimal medium to arginine-supplemented medium. Within an hour after arginine supplementation, the amount of intracellular ornithine (95% of which had been stored in vesicles) dropped by 65%, even though the catabolism of arginine produces as much ornithine as had been produced on minimal medium. The arginine level in the cell rose 10-fold. Ornithine flux through the catabolic enzyme ornithine aminotransferase increased fivefold, but flux through the mitochondrial enzyme ornithine transcarbamylase (leading to arginine synthesis) was only 20% of the rate seen on minimal medium. During this transition to arginine catabolism, the enzymes of the arginine pathway operate as an ornithine cycle, but at a restricted rate. We suggest the hypothesis that high levels of arginine may inhibit the movement of ornithine into the vesicles and into the mitochondria.
mesh_terms: D001120:Arginine / Q000378:metabolism*; D003470:Culture Media; D007700:Kinetics; D008928:Mitochondria / Q000378:metabolism; D009491:Neurospora / Q000378:metabolism*; D009492:Neurospora crassa / Q000201:enzymology / Q000378:metabolism* / Q000648:ultrastructure; D009940:Organoids / Q000378:metabolism; D009952:Ornithine / Q000378:metabolism*; D009954:Ornithine Carbamoyltransferase / Q000378:metabolism; D009953:Ornithine-Oxo-Acid Transaminase / Q000378:metabolism
chemical_list: D003470:Culture Media; D001120:Arginine; D009952:Ornithine; D009954:Ornithine Carbamoyltransferase; D009953:Ornithine-Oxo-Acid Transaminase