Pawelczyk T, Olson M S
Department of Biochemistry, University of Texas Health Science Center, San Antonio 78284-7760.
Arch Biochem Biophys. 1993 Jan;300(1):489-94. doi: 10.1006/abbi.1993.1066.
The activities of the enzyme components of the pyruvate dehydrogenase complex are affected to different extents by changes in ionic strength and pH. At pH 7.4 the optimum activity of pyruvate dehydrogenase (E1), dihydrolipoamide acetyltransferase (E2), and dihydrolipoamide dehydrogenase (E3) occur in the ranges of ionic strengths of 0.06-0.08, 0.01-0.02, and 0.10-0.15 M, respectively. The activity of dihydrolipoamide dehydrogenase is least sensitive to changes in the ionic strength of the assay medium. At constant ionic strength (0.15 M) the optimum activity of E1, E2, and E3 occur at pH 7.4, 7.0, and 8.0, respectively. Changes in pH mostly affect the dihydrolipoamide acetyltransferase activity. Cl- and HCO3- anions inhibit the activity of pyruvate dehydrogenase. In the presence of 80 mM Cl- or HCO3- ions the activity of E1 is inhibited by 25 and 10% respectively. K+, Na+, and HPO4(2-) ions affect the activity of dihydrolipoamide acetyltransferase. The activity of this enzyme component is stimulated by 28 and 25% in the presence of 80 mM K+ and Na+ cations, respectively. HPO4(2-) stimulates the dihydrolipoamide acetyltransferase in a calcium-dependent manner. In the presence of 20 mM HPO4(2-) the activity of the dihydrolipoamide acetyltransferase increases 20 and 40% in the absence and presence of 0.1 mM Ca2+, respectively. The activity of dihydrolipoamide dehydrogenase is not affected by K+, Na+, HPO4(2-), Cl-, or HCO3-.
丙酮酸脱氢酶复合体中酶组分的活性受离子强度和pH值变化的影响程度各异。在pH 7.4时，丙酮酸脱氢酶（E1）、二氢硫辛酰胺乙酰转移酶（E2）和二氢硫辛酰胺脱氢酶（E3）的最佳活性分别出现在离子强度为0.06 - 0.08 M、0.01 - 0.02 M和0.10 - 0.15 M的范围内。二氢硫辛酰胺脱氢酶的活性对测定介质离子强度的变化最不敏感。在恒定离子强度（0.15 M）下，E1、E2和E3的最佳活性分别出现在pH 7.4、7.0和8.0时。pH值的变化主要影响二氢硫辛酰胺乙酰转移酶的活性。Cl⁻和HCO₃⁻阴离子会抑制丙酮酸脱氢酶的活性。在存在80 mM Cl⁻或HCO₃⁻离子时，E1的活性分别被抑制25%和10%。K⁺、Na⁺和HPO₄²⁻离子会影响二氢硫辛酰胺乙酰转移酶的活性。在存在80 mM K⁺和Na⁺阳离子时，该酶组分的活性分别被刺激28%和25%。HPO₄²⁻以钙依赖的方式刺激二氢硫辛酰胺乙酰转移酶。在存在20 mM HPO₄²⁻时，在不存在和存在0.1 mM Ca²⁺的情况下，二氢硫辛酰胺乙酰转移酶的活性分别增加20%和40%。二氢硫辛酰胺脱氢酶的活性不受K⁺、Na⁺、HPO₄²⁻、Cl⁻或HCO₃⁻的影响。
