Atchuta Ramaiah K V, Chen J J, Gallop P M, London I M
Harvard-MIT Division of Health Sciences and Technology, Massachusetts Institute of Technology, 77 Massachusetts Avenue, E25-551, Cambridge, MA 02139, USA.
Blood Cells Mol Dis. 1997 Aug;23(2):177-87. doi: 10.1006/bcmd.1997.0135.
Pyrroloquinoline quinone (PQQ), a novel cofactor of biological redox processes, is ubiquitous in animal cells. We have examined the effects of PQQ on protein synthesis. PQQ inhibits protein synthesis in hemin-supplemented rabbit reticulocyte lysates. This inhibition is characterized by increased phosphorylation of eIF-2alpha and by diminished guanine nucleotide exchange activity of eIF-2B. The increased eIF-2alpha phosphorylation is the result of activation by PQQ of the heme-regulated eIF-2alpha kinase (HRI). The addition of 10 microM PQQ completely inhibits the increase in protein synthesis that occurs on the addition of hemin (20 microM) to heme-deficient lysates, whereas a lower concentration of PQQ (100 nM) causes a very slight stimulation of protein synthesis. The increased eIF-2alpha phosphorylation that occurs at high concentrations of PQQ inhibits eIF-2B activity, presumably due to formation of a 15S complex [eIF-2(alphaP).eIF-2B] in which eIF-2B becomes non-functional. Low concentrations of PQQ (0.1-1 microM) do not affect eIF-2alpha phosphorylation, but rather enhance the guanine nucleotide exchange activity of eIF-2B in reticulocyte lysates. In Chinese hamster ovary cell extract which is devoid of significant eIF-2alpha kinase activity, addition of both low and high concentrations of PQQ results in an increase in eIF-2B activity. The addition of PQQ to reticulocyte lysates activates HRI whereas addition of PQQ to purified HRI in vitro inhibits the autokinase and eIF-2alpha kinase activity of the HRI; the inhibition of purified HRI by PQQ is observed both in the presence and absence of hemin. These findings suggest that PQQ inhibits purified HRI by acting as an oxidant whereas in lysates in which PQQ is readily reduced, the PQQ acts as a reductant and increases the activities of both HRI and eIF-2B.
吡咯喹啉醌（PQQ）是生物氧化还原过程中的一种新型辅因子，在动物细胞中广泛存在。我们研究了PQQ对蛋白质合成的影响。PQQ抑制添加血红素的兔网织红细胞裂解物中的蛋白质合成。这种抑制的特征是eIF-2α磷酸化增加以及eIF-2B的鸟嘌呤核苷酸交换活性降低。eIF-2α磷酸化增加是PQQ激活血红素调节的eIF-2α激酶（HRI）的结果。向血红素缺乏的裂解物中添加10μM PQQ可完全抑制添加20μM血红素后发生的蛋白质合成增加，而较低浓度的PQQ（100 nM）会对蛋白质合成产生非常轻微的刺激。高浓度PQQ时发生的eIF-2α磷酸化增加会抑制eIF-2B活性，推测是由于形成了15S复合物[eIF-2(αP).eIF-2B]，其中eIF-2B失去功能。低浓度的PQQ（0.1 - 1μM）不会影响eIF-2α磷酸化，反而会增强网织红细胞裂解物中eIF-2B的鸟嘌呤核苷酸交换活性。在缺乏显著eIF-2α激酶活性的中国仓鼠卵巢细胞提取物中，添加低浓度和高浓度的PQQ都会导致eIF-2B活性增加。向网织红细胞裂解物中添加PQQ会激活HRI，而在体外向纯化的HRI中添加PQQ会抑制HRI的自身激酶和eIF-2α激酶活性；在有和没有血红素的情况下，PQQ对纯化的HRI均有抑制作用。这些发现表明，PQQ作为氧化剂抑制纯化的HRI，而在PQQ容易被还原的裂解物中，PQQ作为还原剂增加HRI和eIF-2B的活性。
