ROMERO JORGE MIGUEL
Congresos y reuniones científicas
Título:
Reaction Mechanism and Glucosylation Extent of Monomeric and Dimeric Glycogenin Autoglucosylation
Autor/es:
ISSOGIO, F M; CARRIZO, M E; LAFI, I; ROMERO, J M; CURTINO, J A
Lugar:
Buzios, Rio de Janeiro, Brazil
Reunión:
Congreso; VII Iberoamerican Congress of Biophysics; 2009
Institución organizadora:
Brazilian Biophysical Society, Sociedad de Biofisicos Latino Americanos
Resumen:

We have recently described that below 0.8-0.6 mM, the concentration at which glycogenin exists as monomer, the enzyme has the ability to autoglucosylate with a first order kinetics (Biochem, Biophys. Res. Commun. 371:328-332, 2008). Thus, our results indicated that the intersubunit glucosylation of dimeric glycogenin, which was demonstrated by other authors, is not the unique reaction mechanism for the intramolecular glucosylation of its tyrosine residue. In the present work we analyzed whether in the dimer the glycogenin subunit is able to carry out the glucosylation by both, intersubunit and intrasubunit reactions. This study was accomplished using non-glucosylated apo-glycogenin (Gn) and measuring the specific autoglucosylation rate (SAR) of both, the monomer, and the monomer forced to dimerize by mixing with the proper amount of a) Gn mutant having intact glucosilable tyrosine but lacking activity (sGn), or b) a double mutant lacking activity and the substrate tyrosine residue (nGn). We have also analyzed whether any difference existed between monomeric and dimeric glycogenin in the polymerization degree of the linked oligoglucan acquired by full autoglucosylation. The study was carried out by measuring the specific autoglucosylation extent (SAE) of Gn monomer and dimer and of the mixtures of wild type and mutant enzymes above mentioned. The described results are discussed in terms of regulation at the initial step of the de novo glycogen biosynthesis by the glycogenin capacity to display two different reaction mechanisms, and to acquire different autoglucosylation degree.