Rate-limiting steps for the esterase and dehydrogenase reaction catalyzed by horse liver aldehyde dehydrogenase

Horse liver aldehyde dehydrogenase, like other aldehyde dehydrogenases, is capable of hydrolyzing esters such as nitrophenyl acetate. Pre-steady state and burst kinetics were performed using substrate levels of enzyme to determine whether the rate-limiting step occurred prior to or after the formation of an acyl enzyme intermediate. A burst was found by both techniques for the dehydrogenase reaction; but no burst was found for the esterase reaction. These data show that the rate-limiting step for the two reactions catalyzed by the enzyme differs. For dehydrogenase it occurs after the formation of the acyl intermediate, but for esterase it occurs prior to its formation.