On the nature of the carbamyl group donor in citrulline biosynthesis

The viral mechanism of Reye's syndrome

In the initial stages of Reye's Syndrome, following an influenza infection, the viral RNA polymerase activates liver host cell ornithine decarboxylase by combining with this enzyme. Once the reaction has occurred, ornithine decarboxylase is no longer available to combine with and to activate host cell RNA polymerase. The virally activated ornithine decarboxylase removes ornithine from participation in the urea cycle by metabolizing ornithine to putrescine which, in turn, is metabolized to spermidine. Once ornithine has been removed from participation in the urea cycle, mitochondrial carbamoyl phosphate levels increase until the carbamoyl phosphate passes from the mitochondria into the cytosol where it is metabolized by the de novo pyrimidine synthesis pathway. Through the implementation of this process, the virus has insured that: host cell RNA polymerase in liver cells is inactivated, viral RNA polymerase has complete access to newly synthesized pyrimidines, production of pyrimidines for the synthesis of viral messenger RNA is initiated, spermidine, a mRNA stabilizer is produced, many of the components necessary for viral mRNA synthesis are provided by the host cell's RNA synthesizing mechanism.

Urea and its formation in coelacanth liver

Urea occurs in liver of the coelacanth Latimeria chalumnae to the extent of about 1.7 percent by weight. It was determined quantitatively by reaction with 1-phenyl-1,2-propanedione-2-oxime (Archibald reagent) and by measurement of ammonia released upon treatment with urease. Arginase and ornithine carbamoyltransferase, enzymes instrumental in the formation of urea in typical ureotelic vertebrates, occur in homogenates of coelacanth liver. Formed in part by the ornithine-urea cycle, urea may have an osmoregulatory function in the coelacanth as it has in elasmobranchs.