Transiently reduced activity of carbamyl phosphate synthetase and ornithine transcarbamylase in liver of children with Reye's syndrome.

Since Reye's syndrome is associated with hyperammonemia, we measured the urea-cycle enzymes in hepatic tissue of 13 patients. Expressed as nanomoles of citrulline per milligram of hepatic protein per minute, mean activity of carbamyl phosphate synthetase (6.27 +/- 2.45 S.D.) and ornithine transcarbamylase (136.19 +/- 41.83) in Reye's syndrome was reduced significantly (P less than 0.005) when compared with that of 25 "normal" controls (11.54 +/- 4.24 and 307.49 +/- 94.15, respectively). Activity was maximally reduced during the first days of clinical symptoms; it returned toward normal during the following week regardless of whether the disease ended in death or recovery. The activity of the two enzymes was normal in patients with salicylate intoxication or heritable argininosuccinic acid synthetase deficiency. The apparent Km of hepatic ornithine transcarbamylase for ornithine was in the normal range in patients with Reye's syndrome (mean 0.24 mM). These observations indicate that Reye's syndrome is associated with acquired and transient dysfunction of hepatic mitochondrial urea-cycle enzymes.