Isocitrate dehydrogenase constants

The acid is measured using the enzyme isocitrate dehydrogenase. Isocitrate is present in a small but fairly constant amount. Table IV gives the concentrations and ratios with citric acid. 

Roy, S. O., and Packard, T. T. (2001). CO2 production rate predicted from isocitrate dehydrogenase activity, intracellular substrate concentrations and kinetic constants in the marine bacterium Pseudomonas nautica. Mar. Biol. (Berl.) 138, 1251-1258. 

Since the initial rate equation for a random mechanism, Eq. (13), is not of the linear form of Eq. (1), it can account for rate cooperativity with appropriate values for the rate constants (6,30,149) and has been suggested for isocitrate dehydrogenases (lJf2,150). It does not require that there be more than one active center in the enzyme molecule nor cooperative equilibrium binding of substrates or modifiers. An alternative to this purely kinetic explanation is that there are two or more active... 

Alkyl halides are even less reactive than acyl halides, as indicated by the compilation of reaction rates of thiolate anions with various types of alkyl halides (282). Nevertheless, potentially useful affinity labels have been synthesized with alkyl halide substituents and have been shown to specifically inactivate several enzymes, albeit slowly the low reactivity of the alkyl halides may minimize nonspecific reaction. Adenosine 5 -(2-bromoethyl)phosphate has been characterized and reported to inactivate NAD -dependent isocitrate dehydrogenase (283). The 2 - and 3 -(2-bromoethyl)-AMP labels have also been synthesized, and model reactions of the bromoethyl-AMPs with cysteine, lysine, histidine, and tyrosine have been studied (284). More recently, esters of adenosine 5 -monophosphate have been prepared with ethyl, propyl, or hexyl moieties and bromo or chloro substituents at the w position (285). Yeast alcohol dehydrogenase exhibited enhanced inactivation by the hexyl derivative, but inactivation rates of other dehydrogenases were unremarkable. Two iodopropyl derivatives of cAMP have been described, namely, 1, A -(3-iodopropyleno)adenosine 3, 5 -cyclic monophosphate and 3 -0-(2-iodo-3-hydroxypropyl)adenosine 3, 5 -cyclic monophosphate the latter inactivates cAMP phosphodiesterase from human platelets, with a pseudo-first-order rate constant of 0.147 hr" (286). 

For example, in isocitrate dehydrogenase reaction, we shall see the formation of an enzyme-isocitrate-NADH complex because the extra hydrogen is not a problem (Grissom Cleland, 1988). When the common group is larger, such as a phosphate group or bigger, one usually will not see the EAP complex, or the dissociation constants for this complex are elevated. Thus, in the hexokinase reaction... 

Again, as was shown for the malic enzyme, a single enzyme is responsible for both oxidation and decarboxylation oxalosuccinate is decarboxylated by the purest preparation of isocitric dehydrogenase available (247,248). The equilibrium constant ... 

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