Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UMLS:C0038187 (starvation)
 24,951 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

N-Acetylglutamate synthase, an early enzyme of the arginine pathway, provides acetylglutamate for ornithine synthesis in the so-called "acetylglutamate cycle." Because acetylglutamate is regenerated as ornithine is formed, the enzyme has only a catalytic or anaplerotic role in the pathway, maintaining "bound" acetyl groups during growth. We have detected this enzyme in crude extracts of Neurospora crassa and have localized it to the mitochondria along with other ornithine biosynthetic enzymes. The enzyme is bound to the mitochondrial membrane. The enzyme has a pH optimum of 9.0 and Km values for glutamate and CoASAc of 6.3 and 1.6 mM, respectively. It is feedback-inhibited by L-arginine (I0.5 = 0.16 mM), and its specific activity is augmented 2-3-fold by arginine starvation of the mycelium. Mutants of the newly recognized arg-14 locus lack activity for the enzyme. Because these mutants are complete auxotrophs, we conclude that N-acetylglutamate synthase is an indispensible enzyme of arginine biosynthesis in N. crassa. This work completes the assignment of enzymes of the arginine pathway of N. crassa to corresponding genetic loci. The membrane localization of the enzyme suggests a novel mechanism by which feedback inhibition might occur across a semipermeable membrane.
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PMID:N-acetyl-L-glutamate synthase of Neurospora crassa. Characteristics, localization, regulation, and genetic control. 293 69

Translation of bacterial mRNA, divorced from transcription, has been obtained for enzymes of arginine synthesis; evidence has been acquired for repression by arginine at the level of translation. mRNAs for acetylornithinase and ornithine transcarbamylase were accumulated by arginine starvation of argR(+) and argR(-) arginine auxotrophs derived from Escherichia coli K12. Further transcription was inhibited with rifampicin or miracil D, and enzyme formation was measured in the presence of either an excess of, or a restricted supply of, arginine. For the argR(+) strain 961, little mRNA was found without starvation; for the argR(-) strain 977, a considerable amount of mRNA was demonstrated even without starvation. There was relatively little translation for the argR(+) strain, but not for the argR(-) strain, in the presence of excess arginine, apparently due to an accelerated degradation of mRNA in the argR(+) strain under repressive conditions.
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PMID:Translational repression in the arginine system of Escherichia coli. 492 18

Rats fasted for 3 and 6 days showed an increase in the activity, per g of liver but not per total liver, of the mitochondrial urea cycle enzymes, carbamylphosphate synthetase and ornithine transcarbamylase. The activity of N-acetylglutamate synthetase, both per g and per total liver, increased by the third day and then decreased on the sixth day of fasting. The cytosolic enzyme N-acetyldeacylase showed the same general pattern as the N-acetylglutamate synthetase except that the relative proportion of synthetase over deacylase was higher at the third day of starvation. The N-acetylglutamate level/g liver increases in relation to the number of days of fasting.
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PMID:Effect of starvation on the N-acetylglutamate system of rat liver. 685 46