A novel method for determining rate constants for dehydration of aldehyde hydrates.

A method has been developed for calculating rate constants for dehydration of aldehydes that induce ATPase reactions by kinases and where 18O is transferred from the aldehyde or its hydrate to inorganic phosphate during the reaction. The method involves measurement of the fraction of 18O in phosphate by 31P NMR after the ATPase reaction has proceeded for several minutes with zero-order kinetics. The reaction is started by addition of the aldehyde in a small volume of H2 18O, and the speed of washout of 18O by reversible dehydration relative to the rate of the ATPase reaction allows calculation of the rate constants if the hydration equilibrium constant is known from the proton NMR spectrum of the aldehyde. Dehydration rate constants (s-1 at pH 8-8.5, 0.1 M buffer, 25 degrees C) for the following aldehydes (all over 95% hydrated) and kinases used are as follows: D-glyceraldehyde with glycerokinase, 0.03; 2,5-anhydro-D-mannose 6-phosphate with fructose-6-phosphate kinase, 0.025; 2,5-anhydro-D-mannose or 2,5-anhydro-D-talose with fructokinase, 0.029 and 0.017, respectively; D-gluco-hexodialdose with hexokinase, 0.068. With betaine aldehyde and choline kinase or glyoxylate and pyruvate kinase, no 18O was transferred to phosphate during the ATPase reactions. However, the dehydration rate constant for glyoxylate (0.007 s-1 at pH 7 extrapolated to zero buffer concentration and up to 0.11 s-1 at pH 9.0 with 0.3 M buffer) was determined by extrapolating the initial rate of reduction of the free aldehyde catalyzed by lactate dehydrogenase to infinite enzyme levels.(ABSTRACT TRUNCATED AT 250 WORDS)