Gilles-González M A, González G, Perutz M F
Medical Research Council Laboratory of Molecular Biology, Cambridge, United Kingdom.
Biochemistry. 1995 Jan 10;34(1):232-6. doi: 10.1021/bi00001a027.
FixL is a ferrous heme protein whose kinase activity is inhibited by oxygen. Here we show that met-FixL, which is the ferric unliganded form, has the same activity as deoxy-FixL, the ferrous unliganded form, indicating that activity does not depend on the oxidation state of the heme iron. The ferric derivative fluoro-FixL is fully active, indicating that the presence of a heme ligand is not sufficient to cause kinase inhibition. An inverse relation between the rate of autophosphorylation of ferric FixL and the fractional saturation with cyanide shows that the cyanomet form has zero activity. All our active derivatives were high-spin, while our inactive derivatives were low-spin. In mixtures of high- and low-spin FixL, resulting from partial saturation with low-spin ligands, the activity was that which would be expected for the concentration of the high-spin component alone. Therefore the spin state of the heme iron rather than the oxidation state or presence of ligands must be the factor that controls FixL's kinase activity. On transition from low to high spin, the heme iron moves out of the porphyrin plane by 0.4 A. We propose that, as in hemoglobin, this motion triggers a long-range conformational change which in FixL is responsible for a switch to an active form.
FixL是一种亚铁血红素蛋白，其激酶活性受氧气抑制。在此我们表明，高铁无配体形式的met-FixL与亚铁无配体形式的脱氧-FixL具有相同的活性，这表明活性并不取决于血红素铁的氧化态。高铁衍生物氟-FixL具有完全活性，这表明血红素配体的存在不足以导致激酶抑制。高铁FixL的自磷酸化速率与氰化物的分数饱和度之间呈反比关系，表明氰化高铁形式的活性为零。我们所有的活性衍生物都是高自旋的，而无活性衍生物是低自旋的。在由低自旋配体部分饱和导致的高自旋和低自旋FixL混合物中，活性是仅由高自旋成分浓度所预期的活性。因此，血红素铁的自旋状态而非氧化态或配体的存在必定是控制FixL激酶活性的因素。从低自旋转变为高自旋时，血红素铁移出卟啉平面0.4埃。我们提出，与血红蛋白一样，这种移动引发了一种远程构象变化，在FixL中这种变化导致转变为活性形式。
