Effect of pH on the self-exchange reactivity of the plant plastocyanin from parsley |
| |
Authors: | Hunter D M McFarlane W Sykes A G Dennison C |
| |
Institution: | Department of Chemistry, University of Newcastle upon Tyne, Newcastle upon Tyne NE1 7RU, U.K. |
| |
Abstract: | The self-exchange rate constant (25 degrees C) for parsley plastocyanin is 5.0 x 10(4) M-1 s-1 at pH* 7.5 (I = 0.10 M). This value is quite large for a higher plant plastocyanin and can be attributed to a diminished upper acidic patch in this protein. The self-exchange rate constant is almost independent of pH* in the range 7.5-5.6, with a value (25 degrees C) of 5.6 x 10(4) M-1 s-1 at pH* 5.6 (I = 0.10 M). At this pH*, the ligand His87 is protonated in approximately 50% of the reduced protein molecules (pKa* 5.6), and this would be expected to hinder electron transfer between the two oxidation states. However, this effect is counterbalanced by the enhanced association of two parsley plastocyanins at lower pH* due to the partial protonation of the acidic patch. |
| |
Keywords: | |
本文献已被 PubMed 等数据库收录! |
|