title: Ornithine transcarbamylase (OTC) in white blood cells.
abstract: A radiochemical assay method of ornithine transcarbamylase (OTC) was developed using labeled carbamyl phosphate as a substrate. The enzyme activities determined by this method in peripheral white blood cells from ten normal subjects were 1.32 +/- 0.95 nmoles/mg/hr and the apparent Km's, when assayed at pH 8.5, were 6.4 mM for ornithine and 0.6 mM for carbamyl phosphate. On the contrary, the apparent Km's of human liver OTC were 0.6 mM for ornithine and 0.12 mM for carbamyl phosphate. The average OTC activity of granulocytes was 1.0 nmoles/mg/hr, whereas that of mononuclear cells was 0.4 mmoles/mg/hr. Lymphoid cell lines were established from three normal subjects and an OTC-deficient infant. All these cell lines demonstrated no OTC activity. When arginine was removed from the medium and replaced by ornithine, the lymphoid cells were unable to grow in culture. On autoradiography, the lymphoid cells showed labelling at incubation in the presence of 14C-citrulline, but not with 14C-ornithine.
mesh_terms: D000592:Amino Acid Metabolism, Inborn Errors / Q000175:diagnosis; D000641:Ammonia / Q000097:blood; D000818:Animals; D002221:Carbamyl Phosphate; D002250:Carbon Radioisotopes; D002417:Cattle; D002478:Cells, Cultured; D006801:Humans; D007223:Infant; D007962:Leukocytes / Q000201:enzymology*; D008099:Liver / Q000201:enzymology; D009952:Ornithine; D009954:Ornithine Carbamoyltransferase / Q000097:blood*; D020163:Ornithine Carbamoyltransferase Deficiency Disease; D011869:Radioligand Assay / Q000379:methods
chemical_list: D002250:Carbon Radioisotopes; D002221:Carbamyl Phosphate; D000641:Ammonia; D009952:Ornithine; D009954:Ornithine Carbamoyltransferase