Pintus F, Mura A, Rinaldi A C, Contini A, Spanò D, Medda R, Floris G
Department of Applied Sciences in Biosystems, University of Cagliari Cittadella Universitaria, 09042 Monserrato, CA, Italy.
Protein J. 2008 Dec;27(7-8):434-9. doi: 10.1007/s10930-008-9153-0.
Activity assays, conformational changes and transitional switches between secondary structures of a peroxidase from Euphorbia characias were studied in the presence of trifluoroethanol and in the presence or absence of calcium ions. The addition of trifluoroethanol up to 10-20% first induced a drastic decrease of alpha-helix content followed by an increase of tryptophan fluorescence emission intensity, a progressive re-induction of the formation of alpha-helical elements concomitant with loss of enzyme activity. In the presence of calcium ions, the fluorescence of the enzyme almost remained unchanged in the trifluoroethanol concentration range 5-20%. Further increase in trifluoroethanol concentration led to a protein structure characterized by a progressive re-induction of alpha-helical elements, a remarkable increase of the tryptophan fluorescence and a loss of enzyme activity. These results indicate that calcium ions in Euphorbia peroxidase play an essential role in maintaining the hydrophobic interactions on the protein structure preserving enzymatic activity.
在三氟乙醇存在的情况下，以及在有或没有钙离子的情况下，研究了来自大戟属植物的过氧化物酶的活性测定、构象变化和二级结构之间的转变开关。添加高达10%-20%的三氟乙醇首先导致α-螺旋含量急剧下降，随后色氨酸荧光发射强度增加，伴随着酶活性丧失，α-螺旋元件形成逐渐重新诱导。在存在钙离子的情况下，在5%-20%的三氟乙醇浓度范围内，酶的荧光几乎保持不变。三氟乙醇浓度的进一步增加导致蛋白质结构的特征是α-螺旋元件逐渐重新诱导、色氨酸荧光显著增加以及酶活性丧失。这些结果表明，大戟属过氧化物酶中的钙离子在维持蛋白质结构上的疏水相互作用以保持酶活性方面起着至关重要的作用。
