De Baere I, Perutz M F, Kiger L, Marden M C, Poyart C
Medical Research Council Laboratory of Molecular Biology, Cambridge, England.
Proc Natl Acad Sci U S A. 1994 Feb 15;91(4):1594-7. doi: 10.1073/pnas.91.4.1594.
We have tried to find out why Ascaris hemoglobin has such an exceptionally high oxygen affinity (P50 approximately 0.004 mmHg; 1 mmHg = 133 Pa). Following Kloek et al., we have synthesized the N-terminal globin domain of Ascaris hemoglobin in Escherichia coli [Kloek, A. P., Yang, J., Mathews, F. S. & Goldberg, D. (1993) J. Biol. Chem. 268, 17669-17671]. Like Kloek et al., we found its oxygen affinity to be as high as that of native Ascaris hemoglobin. We thought that this high affinity might be due to the heme-bound oxygen molecule being stabilized by two hydrogen bonds from the globin instead of the usual one. Ascaris hemoglobin has a distal glutamine instead of the more usual histidine as one of the potential hydrogen bond donors. In addition, it contains a tyrosine at position 10 of B helix (B10) in place of the leucine generally found there in vertebrate myoglobins and hemoglobins. Following the discovery of Carver et al. that sperm whale myoglobin with the replacement of leucine B10 by phenylalanine has a raised oxygen affinity, we have replaced tyrosine B10 in the N-terminal domain of Ascaris hemoglobin by either leucine or phenylalanine [Carver, T. E., Brantley, R. E., Jr., Singleton, E. W., Arduini, R. M., Quillin, H. L., Phillips, G. N., Jr., & Olson, J. S. (1992) J. Biol. Chem. 267, 14443-14450]. Either of these replacements lowered the oxygen affinity about 100-fold, to the same level of that of human alpha-globin chains. These results are consistent with a hydrogen bond linking the tyrosine hydroxyl to the heme-linked oxygen, with a bond energy of 2.7 kcal/mol.
我们试图找出蛔虫血红蛋白为何具有如此异常高的氧亲和力（P50约为0.004 mmHg；1 mmHg = 133 Pa）。按照克洛埃克等人的方法，我们在大肠杆菌中合成了蛔虫血红蛋白的N端珠蛋白结构域[克洛埃克，A.P.，杨，J.，马修斯，F.S.和戈德堡，D.（1993年）《生物化学杂志》268，17669 - 17671]。和克洛埃克等人一样，我们发现其氧亲和力与天然蛔虫血红蛋白一样高。我们认为这种高亲和力可能是由于血红素结合的氧分子由来自珠蛋白的两个氢键而非通常的一个氢键稳定。蛔虫血红蛋白有一个远端谷氨酰胺而非更常见的组氨酸作为潜在的氢键供体之一。此外，它在B螺旋的第10位（B10）含有一个酪氨酸，取代了脊椎动物肌红蛋白和血红蛋白中通常在该位置发现的亮氨酸。在卡弗等人发现用苯丙氨酸取代亮氨酸B10的抹香鲸肌红蛋白具有升高的氧亲和力之后，我们用亮氨酸或苯丙氨酸取代了蛔虫血红蛋白N端结构域中的酪氨酸B10[卡弗，T.E.，布兰特利，R.E.，小，辛格尔顿，E.W.，阿尔杜伊尼，R.M.，奎林，H.L.，菲利普斯，G.N.，小，和奥尔森，J.S.（1992年）《生物化学杂志》267，14443 - 14450]。这两种取代中的任何一种都使氧亲和力降低了约100倍，降至与人类α - 珠蛋白链相同的水平。这些结果与酪氨酸羟基与血红素连接的氧之间存在一个氢键一致，键能为2.7千卡/摩尔。
