The role of N-carbamyl, N-acetyl, and L-glutamic acids with and without fumaric acid on the "in vitro" synthesis of citrulline was studied by using a particulate fraction obtained from a rat liver homogenate and a partially purified citrulline-synthesizing enzyme system. In the presence of a particulate fraction of rat liver homogenate, N-carbamyl and N-acetyl-L-glutamic acids are unable to replace L-glutamic acid, which is essential for citrulline biosynthesis. However, in the presence of fumaric acid, they both give a better synthesis of citrulline than L-glutamic acid alone. It is postulated that the acyl derivatives serve only in the transport of "activated CO2" whereas fumaric acid enters the citric acid to furnish the essential ATP molecules. Glutamic acid would be able to perform both functions. However, in the presence of a system containing partially purified citrulline-synthesizing enzymes, L-glutamic acid is unable to replace N-carbamyl and N-acetyl-L-glutamic acids with or without fumaric acid. In such a system, L-glutamic acid cannot serve in the transport of "activated CO2". It is postulated that L-glutamic acid must be acetylated prior to its utilization in this respect.With the particulate fraction of rat liver homogenate, N-allyl aspartic acid inhibits totally the synthesis of citrulline both in the presence and absence of fumaric acid with or without glutamic or N-acetyl glutamic acids. It probably interferes with the transport of "activated CO2".
Retinyl palmitate hydrolase activity in normal rat liver.
