Investigations of protein–solute interactions typically show that osmolytes favor native conformations. In this study, the effects of representative compatible and counteracting osmolytes on the reactivationof lactate dehydrogenase from two different conformational states were explored. Contrary to expectations, proline and trimethylamine oxide inhibited both the initial time course and the extent of reactivation of lactate dehydrogenase from bovine heart following dena-turation in guanidine hydrochloride, as well as following inactivation at pH . Reactivation of acid-dissociated porcine heart lactate dehydrogenase was inhibited by both proline and trimethylamine oxide (2M). In all instances, trimethylamine oxide was the more effective inhibitor of reactivation. .
