Altered enolase in aged Turbatrix aceti results from conformational changes in the enzyme

Young- and old-type enolases (2-phospho-D-glycerate hydrolyase, EC 4.2.1.11) from the free-living nematode Turbatrix aceti can be unfolded in 1.25 M guanidine hydrochloride and subsequently refolded with essentially a quantitative recovery. After refolding, both enolases form an identical or near-identical third type of the enzyme as determined by spectral criteria, sensitivity to heat, immunotitration, and rate of inactivation by bacterial protease. By the same criteria, the refolded enolase is closer in conformation to the native old form of the enzyme than to the young form. The results prove that young and old enolases are conformational isomers and that an in vivo transformation from young to old enzyme takes place by conformational changes without covalent modification. The process may be related to the previously demonstrated slowing of enolase turnover in T. aceti. Errors in sequence cannot be involved in the age-related alteration of the enzyme.