Norvaline is a non-proteinogenic unbranched-chain amino acid.
Arginine is known as a conditionally essential amino acid (elevated to ‘essential amino acid’ status under certain conditions) due to, in otherwise healthy persons, arginine homeostasis being somewhat maintained following prolonged dietary deprivation.
An arginine deficiency (which can be induced by increasing the activity of the arginase enzyme that converts arginine to ornithine) impairs B-cell function (immunity) and impairment of both hair and muscle growth. Neuromuscular function may also be impaired.
Protein structures (such as enzymes) that require arginine or are otherwise rich in arginine do not appear to be significantly modified.