Glycine is the simplest amino acid and is the only amino acid that is not optically active (it has no stereoisomers). This amino acid is essential for the biosynthesis of nucleic acids as well as of bile acids, porphyrins, creatine phosphate, and other amino acids. On a molar basis, glycine is the second most common amino acid found in proteins and enzymes being incorporated at the rate of 7.5 percent compared to the other amino acids. Glycine is also similar to gamma-aminobutyric acid and glutamic acid in the ability to inhibit neurotransmitter signals in the central nervous system.