N-Glycolylneuraminic Acid (NGNA)

N-Glycolylneuraminic acid (Neu5Gc) is a sialic acid molecule found in most mammals. Humans cannot synthesize Neu5Gc because the human gene CMAH is irreversibly mutated, though it is found in apes. It is absent in human tissues because of inactivation of gene encoding CMP-N-acetylneuraminic acid hydroxylase. The gene CMAH encodes for CMP-N-acetylneuraminic acid hydroxylase, which is the enzyme responsible for CMP-Neu5Gc from CMP-N-acetylneuraminic (CMP-Neu5Ac) acid. This loss of the CMAH was estimated to have occurred two to three millions of years ago, which occurred just before the emergence of the genus Homo. Neu5Gc is closely related to the commonly known N-acetylneuraminic acid (Neu5Ac). Neu5Ac differs by a single oxygen atom that is added in the cytosol of a cell. In many mammals, both of these molecules are transferred into the Golgi so that they may be added to many glycoconjugates.