Liu X Y, Cottrell K O, Nordlund T M
Photochem Photobiol. 1989 Dec;50(6):721-31. doi: 10.1111/j.1751-1097.1989.tb02902.x.
The effects of citrate ion concentration and pH on the optical spectra and fluorescence decay have been measured for several tyrosine model compounds and lima bean trypsin/chymotrypsin inhibitor, a protein containing one tyrosine at position 69 and seven disulfides but no tryptophan, in order to determine the location and environment of Tyr 69. Tyrosine in the protein is protected from citrate collisional quenching, as indicated by the dynamic quenching constant 9 to 15 times smaller than those for the model peptides. Static quenching remains, with a Stern-Volmer constant of about 1.0 M-1, somewhat smaller than those of L-tyrosine, tyrosine-glutamate, and leucine-tyrosine-leucine. The elevated pKa of Tyr 69, greater than or equal to 11.6, also indicates protein protection from solvent ions. Though Coulomb repulsion of the Glu 70/citrate pair may play a role in the shielding of Tyr 69 from citrate, our measurements indicate that steric effects of the protein structure are more important. Tyrosinate emission in the protein at neutral pH is minimal.
为了确定第69位酪氨酸（Tyr 69）的位置和环境，我们测量了几种酪氨酸模型化合物以及利马豆胰蛋白酶/胰凝乳蛋白酶抑制剂（一种在第69位含有一个酪氨酸且有七个二硫键但不含色氨酸的蛋白质）中柠檬酸根离子浓度和pH值对其光谱和荧光衰减的影响。蛋白质中的酪氨酸受到保护，免受柠檬酸碰撞猝灭，动态猝灭常数比模型肽小9至15倍就表明了这一点。静态猝灭仍然存在，斯特恩-沃尔默常数约为1.0 M-1，略小于L-酪氨酸、酪氨酸-谷氨酸和亮氨酸-酪氨酸-亮氨酸的常数。Tyr 69升高的pKa（大于或等于11.6）也表明蛋白质受到保护，免受溶剂离子的影响。虽然Glu 70/柠檬酸对的库仑排斥可能在保护Tyr 69免受柠檬酸影响方面起作用，但我们的测量表明蛋白质结构的空间效应更重要。在中性pH值下，蛋白质中酪氨酸盐的发射最小。
