Carbamyl phosphate synthetase and ornithine transcarbamylase activities in enzyme-deficient human liver measured by radiochromatography and correlated with outcome.
Sensitive and specific radiochromatographic methods to measure enzymatic activities of carbamyl phosphate synthetase I (CPS I) and ornithine transcarbamylase (OTC) were developed. The activities of these enzymes were assayed in frozen liver tissue obtained from 23 individuals with hyperammonemia caused by CPS I (five patients) and OTC deficiency (18 patients). In addition, livers of one aborted fetus with OTC deficiency and four normal individuals were studied. The assays use radioactive ornithine as a substrate followed by separation of citrulline formed in the reactions by HPLC and quantitation of the radioactivity in both amino acids by a radioactivity flow monitor or by a scintillation counter. Both CPS I and OTC assays were linear with respect to length of incubation time and concentration of tissue homogenate. The sensitivity of the methods allowed measurements of CPS I and OTC activities as low as 0.1 mumol/g/min on 5 mg of liver tissue and the diagnosis of CPS I or OTC deficiency could be established on as low as 0.5 and 0.05 mg of tissue, respectively. CPS I activity in different sections of four normal livers was 3.01 +/- 0.16 mumol/g/min (mean +/- SEM, n = 19) and OTC activity was 93.4 +/- 6.3 (mean +/- SEM, n = 19). Residual enzymatic activity could be detected and measured in the liver tissues of one of the five subjects with CPS I deficiency and in 14 of 19 subjects with OTC deficiency. OTC/CPS I activity ratio in normal liver tissue was 31.2 +/- 1.3 (mean +/- SEM, n = 19), whereas this ratio ranged from 343 to greater than 5000 in CPS I deficient livers and from less than 0.02 to 1.55 in OTC deficient livers.(ABSTRACT TRUNCATED AT 250 WORDS)
Tuchman
M
M
Department of Pediatrics, University of Minnesota, Minneapolis 55455.
Tsai
M Y
MY
Holzknecht
R A
RA
Brusilow
S W
SW
D000592:Amino Acid Metabolism, Inborn Errors / Q000097:blood / Q000201:enzymology*; D000641:Ammonia / Q000097:blood*; D002222:Carbamoyl-Phosphate Synthase (Ammonia) / Q000032:analysis* / Q000172:deficiency; D002851:Chromatography, High Pressure Liquid; D006801:Humans; D008099:Liver / Q000201:enzymology*; D009954:Ornithine Carbamoyltransferase / Q000032:analysis*; D020163:Ornithine Carbamoyltransferase Deficiency Disease
D000641:Ammonia; D009954:Ornithine Carbamoyltransferase; D002222:Carbamoyl-Phosphate Synthase (Ammonia)