Glycogenin (GN) is a glucosyltransferase involved in the de novo biosynthesis of glycogen. Two different reaction mechanisms have been proposed for retaining glycosyltransferases such as GN: a double displacement (S_N2) with a short-lived glycosyl-enzyme intermediate, and a single front-side displacement (S_Ni). The molecular nature of GN autoglucosylation is discussed since its crystallographic structure was described, because the distances measured between the amino acids involved in both mechanisms are long enough to preclude them. So, in order to understand at a molecular level the autoglucosylation of GN, the dynamic behaviour of the protein should be considered. Therefore, we performed a molecular dynamics study to analyze GN dimer movement. From the obtained trajectories, we calculated the distances between the amino acids involved in both mechanisms, considering an intra-monomeric reaction or an inter-monomeric one. Our preliminary results suggest that the dynamic behaviour of the protein favours S_Ni reaction mechanism. In agreement with in vitro experimental results, we also found that dimeric GN is more efficient to catalyze its autoglucosylation than the monomer.