Alanine is a non-essential amino acid that is involved in the metabolism of tryptophan and the vitamin pyridoxine. The alpha-carbon in alanine is substituted with a levorotatory (l)-methyl group, making it one of the simplest amino acids with respect to molecular structure. This amino acid is one of the most widely used in protein construction, averaging about 9 percent of average protein composition on a per-mole basis when compared with the other amino acids. Alanine has little therapeutic role in humans, although it has been demonstrated to display a cholesterol-reducing effect in rats.