Gene sequences suggest inactivation of alpha-1,3-galactosyltransferase in catarrhines after the divergence of apes from monkeys.

The glycosylation enzyme alpha-1,3-galactosyltransferase (alpha 1,3GT; UDPgalactose:beta-D-galactosyl-1,4-N-acetyl-D-glucosaminide alpha-1,3-galactosyltransferase, EC 2.4.1.151) displays a unique pattern of distribution in mammals. It synthesizes an abundance of Gal(alpha 1-3)Gal(beta 1-4)GlcNAc-R (alpha-galactosyl) epitopes within the Golgi apparatus of cells of nonprimate mammals, prosimians, and New World monkeys (platyrrhines). The catarrhines, which include Old World monkeys, apes, and humans, lack this enzyme activity because of the inactivation of the alpha 1,3GT gene. In contrast, the catarrhines produce large amounts of antibodies, designated anti-Gal, against the alpha-galactosyl epitope. The inactivation of the alpha 1,3GT gene in ancestral catarrhines was probably the result of an intensive evolutionary pressure for alteration in the makeup of cell surface carbohydrates (i.e., suppression of alpha-galactosyl epitope expression) and for the production of the anti-Gal antibody. To determine the period in which the alpha 1,3GT gene was inactivated in ancestral catarrhines, comparative sequencing of a 370-base-pair region of this gene was performed by polymerase chain reactions with DNA of various primates. The data suggest that alpha 1,3GT inactivation occurred rather late in the course of catarrhine evolution (less than 28 million years ago), as separate events in apes and in Old World monkeys, after the two groups diverged from each other.