The control of pyruvate kinases of Escherichia coli: further studies of the enzyme activated by ribose-5-phosphate
Mort, J.S.; Sanwal, B.D.
Canadian Journal of Biochemistry 56(6): 647-653
ISSN/ISBN: 0008-4018 PMID: 27294 DOI: 10.1139/o78-097
The pyruvate kinase activated by ribose-5-phosphate from Escherichia coli has been purified to homogeneity, taking advantage of the stabilization of the enzyme by its inhibitor phosphate and by thiol reagents. The native enzyme has a tetrameric quaternary structure which, while prone to dissociation under many conditions, remains intact in the presence of the above reagents. The enzyme was found to reactivate on dilution out of 8 M urea. Interestingly, the recovery of activity is greatly increased by phosphate, an allosteric inhibitor, but markedly reduced by the allosteric activator, ribose-5-phosphate, implying that it is harder for the enzyme to refold to a 'relaxed state.' Proteolysis studies indicate a more open structure in the presence of the activator.