Non-additive counteraction of KCI-perturbation of lactate dehydrogenase by trimethylamine N-oxide

Added KCl increases the apparent Michaelis constant (K-m) of pyruvate for porcine muscle-type lactate dehydrogenase (100 mM KCl, 83%; 200 mM KCI, 188%). The effects of 100 mM KCI were fully reversed by 375 mM trimethylamine N-oxide (TMAO). TMAO (375-750 mM) partially reversed the effects of 200 mM KCI. TMAO as the sole solute, at concentrations up to 750 mM, had no effect on K-m. This is atypical because compensatory osmolytes such as TMAO characteristically counteract protein perturbation in an additive manner.