The enzymatic reaction consists of two chemical steps, galactosylation (k2) and degalactosylation (k3). Galactosylation is the first chemical step in the reaction where Glu461 donates a proton to a glycosidic oxygen, resulting in galactose covalently bonding with Glu537. In the second step, degalactosylation, the covalent bond is broken when Glu461 accepts a proton, replacing the galactose with water. Two transition states occur in the deep site of the enzyme during the reaction, once after each step. When water participates in the reaction, galactose is formed, otherwise, when D-glucose acts as the acceptor in the second step, transgalactosylation occurs . It has been kinetically measured that single tetramers of the protein catalyze reactions at a rate of 38,500 ± 900 reactions per minute. Monovalent potassium ions (K+) as well as divalent magnesium ions (Mg2+) are required for the enzyme's optimal activity. The beta-linkage of the substrate is cleaved by a terminal carboxyl group on the side chain of a glutamic acid.