Molecular Characterization of the Glycated Plasma Membrane Calcium Pump”.

GONZÁLEZ FLECHA, F.L.; CASTELLO, P.R.; GAGLAIRDINO, J.J.; ROSSI, J.P.F.C.

JOURNAL OF MEMBRANE BIOLOGY

Springer Verlag

Lugar: New York; Año: 1999 vol. 1 p. 25 - 34

0022-2631

Abstract. We have previously demonstrated (Diabetes39:707–711, 1990) that in vitro glycation of the red cellCa2+ pump diminishes the Ca2+-ATPase activity of theenzyme up to 50%. Such effect is due to the reaction ofglucose with lysine residues of the Ca2+ pump (Biochem.J. 293:369–375, 1993). The aim of this work was todetermine whether the effect of glucose is due to a fullinactivation of a fraction of the total population of Ca2+pump, or to a partial inactivation of all the molecules.Glycation decreased the Vmax for the ATPase activityleaving unaffected the apparent affinities for Ca2+, calmodulinor ATP. The apparent turnover was identical inboth, the glycated and the native enzyme. Glycation decreasedthe Vmax for the ATP-dependent but not for thecalmodulin-activated phosphatase activities. Concomitantlywith the inhibition, up to 6.5% of the lysine residueswere randomly glycated. The probabilistic analysisof the relation between the enzyme activity and the fractionof nonmodified residues indicates that only one Lysresidue is responsible for the inhibition. We suggest thatglucose decreases the Ca2+-ATPase activity by reactingwith one essential Lys residue probably located in thevicinity of the catalytic site, which results in the fullinactivation of the enzyme. Thus, Ca2+-ATPase activitymeasured in erythrocyte membranes or purified enzymepreparations preincubated with glucose depends on theremaining enzyme molecules in which the essential Lysresidue stays unglycated.