Aldehyde Michaelis constant

With this protocol, ping pong reactions will yield at least one plot containing parallel lines. However, it is difficult with this procedure to obtain values for a number of the kinetic parameters (eg., Michaelis constants) for the reaction. An example of a system studied with this procedure is provided by E. coli CoA-linked aldehyde dehydrogenase. See Frieden Protocol... 

A low enantiomeric excess of a reduced product can result from the inability of the oxidoreduc-tase to recognize the structural features of the substrate enantio- and diastereoselectively45. By far the more common case is the competition of two or more enzymes with different enantiose-lectivities and Michaelis constants for the substrate. Yeast cells not only contain yeast alcohol dehydrogenase but several enzymes that arc able to catalyze reductions. At least three different enzymes capable of reducing /i-keto esters have been purified, of which two have D- and one has L-selectivity62-65. Yeast alcohol dehydrogenase has a rather narrow selectivity for short-chain alcohols and aldehydes and certainly is not the catalyst in many of the reductions performed with yeasts. 

Table 2.21. Michaelis constants for aldehyde dehydrogenase (ALD) from various sources...

The Michaelis complexes of the holoenzyme with the aldehyde or the diphos-phoglycerate, and the acylenzyme with orthophosphate, are not included in the scheme because their dissociation constants are too high for their accumulation. 

The simplest of the aldehydes is formaldehyde, whose oxidation by Ce(IV) in 2.0 M perchlorate media has been studied by Husain (1977). It is presumed that formaldehyde exists as a ketohydrate in acid solution (the hydration constant is lO M ). Michaelis-Menten kinetics describe the results, indicating the formation of a precursor complex. A detailed mechanism permits a calculation of the equilibrium quotients for formation of the Ce(IV)-formohydrate complex and the ionization of a... 

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