The central role of Arginine (If this is messy go to the conclusion note)
The adrenals also play a role in the synthesis of arginine.
I have selected a few quotes from an article called “Argininosuccinate synthase: at the center of arginine metabolism” from the International Journal of Biochemical Molecular Biology see- ( http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3074183/
Mammals at the newborn stage use their intestines to produce a product called argininosuccinate synthase. This is necessary as the mother’s milk is naturally low in arginine, a non-essential amino acid.
Producing argininosuccinate synthase from the fetal intestine allows the baby to produce arginine.
“At about two to three years of age, the intestine loses the ability to synthesize arginine as a consequence of the loss of argininosuccinate synthase expression. Subsequently, endogenous arginine biosynthesis becomes an inter-organ process, where the net production of citrulline occurs almost exclusively in the enterocytes of the small intestine and absorption of citrulline from circulation takes place essentially in the cortex of the kidney where it is converted to arginine”.
“Arginine is required by all tissues in the human body for protein synthesis, and by some tissues for specialized needs”. “There are five major pathways in which argininosuccinate synthase plays a key role. These are (a) urea synthesis, (b) nitric oxide synthesis, (c) polyamine synthesis, (d) creatine synthesis, and (e) the de novo synthesis of arginine to maintain serum levels”.
“Arginase splits the arginine to ornithine and urea, which ensures that the arginine generated by the actions of argininosuccinate synthase and argininosuccinate lyase is, for the most part, directed to urea production. Urea is excreted and the ornithine is transported back into the mitochondria to complete the cycle”.
“Argininosuccinate lyase catalyzes the cleavage of argininosuccinate to produce arginine and fumarate". (NOTE-*Fumarate esters are the basis of a recent treatment for MS.)
Argininosuccinate synthase is also involved in nitric oxide metabolism. “Endothelial nitric oxide synthase (eNOS) utilizes L-arginine as the principal substrate, converting it to L-citrulline and nitric oxide. L-citrulline is recycled to L-arginine by two enzymes, argininosuccinate synthase and argininosuccinate lyase, providing the essential arginine for nitric oxide production in endothelial cells . Together, the three enzymes, eNOS, argininosuccinate synthase and argininosuccinate lyase, make up the citrulline- nitric oxide cycle”.
“In adults, the majority of endogenous arginine synthesis involves the intestinal/renal axis. Citrulline is released by the intestines followed by uptake in the kidney. In the kidneys, expression of argininosuccinate synthase and argininosuccinate lyase then promotes conversion of citrulline to arginine and its subsequent release into plasma “.
Conclusion- As we can see, in a healthy system, which matures, the expression of arginiosuccinate synthase switches from dominance by the intestines to the renal/kidney system. If this latter system fails to operate efficiently the cycle is disrupted and the body will make a compensating response. It is this response that matters. Let us not fret about this but simply accept that the healthy path to maturity is not operating as it should and is awry at an important stage of development.