Evidence for tissue specific alterations in Zn2+-induced conformational changes in fructose-bisphosphatase of...

In vitro studies on Zn2+-induced modulations in certain allosteric control of fructose-1,6-bisphosphatase (FBPase: EC 3.1.3.11), isolated from liver and muscle of 28- and 97-wk old rats were carried out in parallel. Similar chromatographic elution on ion-exchanger and electrophoretic mobility on polyacrylamide gels revealed similarity in charge and molecular size of the enzyme proteins from the two ages of rats. Regarding Zn2+ induced modulations, almost all the parameters used did not show any age-dependent significant alteration with liver enzyme. However, in case of muscle FBPase, apart from a significant increase in Ki for ZnCl2, Zn2+-induced modulations in substrate affinity and AMP inhibition were observed to be altered markedly with the enzyme of 97-wk-old rats in comparison to that of 28-wk-old rats. Thus, it suggests age-associated alterations in Zn2+-mediated conformational modification in the muscle enzyme. This has been further supported by tissue-specific usual pattern of substrate affinity in the absence of Zn2+ and exhibition of normal AMP inhibition after replacement of Zn2+ by EDTA. Such age-dependent changes induced by Zn2+ in muscle FBPase may be of high physiological significance with advancing age of the animal.