A fatal variant of human ornithine carbamoyltransferase is stimulated by Mg2+.
Biochemical studies of a female who died at 2 years of age from a possible genetic variant of ornithine carbamoyltransferase (OCTase) deficiency are reported. The patient had severe psychomotor retardation with plasma ammonia levels throughout life reaching as high as 500 mumole/liter. The average OCTase level in the patient's liver was 2% of that in normal livers. Preincubation with 0.05 M MgCl2 resulted in a 570% increase in OCTase activity (13% of control). Citrate synthase and carbamoyl-phosphate synthase I were present at essentially normal levels. Unusual Mg2+ requirements have not been recognized in previous reports of OCTase deficiency, suggesting a genetic variant in this patient.
D000592:Amino Acid Metabolism, Inborn Errors / Q000201:enzymology / Q000235:genetics; D000641:Ammonia / Q000097:blood; D002675:Child, Preschool; D005260:Female; D014644:Genetic Variation; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008099:Liver / Q000201:enzymology; D008274:Magnesium / Q000494:pharmacology; D009154:Mutation; D009954:Ornithine Carbamoyltransferase / Q000235:genetics* / Q000378:metabolism; D020163:Ornithine Carbamoyltransferase Deficiency Disease
D000641:Ammonia; D009954:Ornithine Carbamoyltransferase; D008274:Magnesium