| Abstract: | Studies of the alpha-ketoglutarate dehydrogenase complex have demonstrated that inorganic phosphate ions cause a decrease in the Km value for alpha-ketoglutarate without changing the maximum reaction rate. In the absence of phosphate (tris-HCl buffer) at low concentrations of alpha-ketoglutarate there are some indications of enzyme-substrate cooperative interactions (the Hill coefficient is 1,6). The cooperativity is removed by ADP, which increases the apparent affinity of the enzyme for alpha-ketoglutarate. Upon divalent cations binding to EDTA in the presence of high (20 mM) concentrations of alpha-ketoglutarate the reaction rate is decreased only by 20%, while the value of Km for the given substrate shows a sharp rise. The nature of Mg2+, Ca2+, Ba2+ and Mn2+ effects on the alpha-ketoglutarate dehydrogenase complex activity depends on their concentration. |
