The ARG1 gene provides instructions for producing the enzyme arginase. This enzyme participates in the urea cycle, a series of reactions that occurs in liver cells. The urea cycle processes excess nitrogen, which is generated when proteins and their building blocks (amino acids) are used by the body. Through the urea cycle, excess nitrogen is made into a compound called urea that is excreted by the kidneys. Excreting the excess nitrogen prevents it from accumulating in the form of ammonia, which is toxic.
Arginase controls the last step of the urea cycle, a reaction in which nitrogen is removed from the amino acid arginine and processed into urea for excretion from the body. A compound called ornithine is also produced in this reaction; it is needed for the urea cycle to repeat.
Approximately 12 mutations have been identified in the ARG1 gene. A mutated ARG1 gene may result in an arginase enzyme that is unstable, shorter than usual or the wrong shape, or may prevent the enzyme from being produced at all.
The shape of an enzyme affects its ability to control a chemical reaction. If the arginase enzyme is misshapen or missing, it cannot fulfill its role in the urea cycle. Excess nitrogen is not converted to urea for excretion, and ammonia and arginine accumulate in the body. Ammonia is toxic, especially to the nervous system, and the accumulation of ammonia and arginine are believed to cause the neurological problems and other signs and symptoms of arginase deficiency.
- arginase, liver
- arginase, type I