Dunathan H C, Voet J G
Proc Natl Acad Sci U S A. 1974 Oct;71(10):3888-91. doi: 10.1073/pnas.71.10.3888.
Several pyridoxal-phosphate-dependent enzymes can convert the bound cofactor to pyridoxamine phosphate. This conversion may be an obligatory part of the normal catalytic sequence, as with transaminases, or may be an abnormal path, inactivating the enzyme. This conversion requires protonation of the C(4)' carbon of the cofactor, which has now been shown to proceed stereospecifically and with the same absolute stereochemistry in seven quite different pyridoxal-phosphate enzymes. We report on one of these, tryptophan synthase B protein. This regularity in protonation stereochemistry suggests a remarkable regularity in the geometry of cofactor binding to the apoenzyme. This regularity is interpreted as evidence for the evolution of this entire family of enzymes from a common progenitor which, through the course of evolution, could not invert its original, arbitrary binding stereochemistry without passing through catalytically inactive conformations.
几种依赖磷酸吡哆醛的酶可将结合的辅因子转化为磷酸吡哆胺。这种转化可能是正常催化序列的必要组成部分，如转氨酶那样，也可能是使酶失活的异常途径。这种转化需要辅因子C(4)' 碳的质子化，现已证明在七种截然不同的依赖磷酸吡哆醛的酶中，该过程具有立体特异性且绝对立体化学相同。我们报道其中一种酶，即色氨酸合酶B蛋白。质子化立体化学的这种规律性表明辅因子与脱辅酶结合的几何结构具有显著规律性。这种规律性被解释为该酶家族从共同祖先进化而来的证据，在进化过程中，如果不经过催化无活性的构象，其原始的、任意的结合立体化学就无法反转。
