MECHANISM OF THE PQQ-DEPENDENT METHANOL DEHYDROGENASE

除了烟酰胺和黄素依赖性的脱氢酶外， 是第三类被称为醌蛋白的辅酶， 新的辅因子吡咯并喹啉醌（PQQ）。而PQQ和醌蛋白 最初是在甲基营养菌中发现的，现在 在自然界中广泛分布。除了有 quinoprotein激酶，PQQ已被确定为辅酶在 偶联伯胺氧化的含铜胺氧化酶 胺与O2还原成H2 O2;含PQQ的胺氧化酶具有 在细菌、植物和哺乳动物中被发现。此外，近期数据显示， 表明PQQ是小鼠营养需要。显然，PQQ和 醌蛋白在自然界中起着多种多样的重要作用。 在甲基营养细菌中，PQQ依赖性甲醇脱氢酶（MDH） 从甲醇的氧化中直接通过 电子传递链到O2;该过程是化学耦合的 从ADP和Pi合成ATP。PQQ保持酶结合 在整个MDH催化循环中，被认为是作为2 e-/2 H + 载体，并直接与伯醇底物相互作用。 然而，关于MDH的催化机制的数据很少。的 本提案的总体目标是了解催化机制 的PQQ依赖MDH从扭脱甲基杆菌AM 1。具体地说， 这里提出的实验将定义PQQ的作用， 伯醇底物的氧化并鉴定化学形式 PQQ结合的中间体的机制。本计划的执行将 有助于我们全面了解PQQ依赖的机制， 内切酶

In addition to the nicotinamide- and flavin-dependent dehydrogenases, there is a third class of dehydrogenases called quinoproteins that contain the novel cofactor pyrroloquinoline quinone (PQQ). While PQQ and quinoproteins were first characterized in methylotrophic bacteria, they are now recognized to be widely distributed in nature. In addition to the quinoprotein dehydrogenases, PQQ has been identified as the cofactor in the copper-containing amine oxidases which couple the oxidation of primary amines with the reduction of O2 to H2O2; PQQ-containing amine oxidases have been identified in bacteria, plants, and mammals. In addition, recent data indicate that PQQ is a nutritional requirement in mice. Clearly, PQQ and quinoproteins play a diverse and important role in nature. In methylotrophic bacteria, the PQQ-dependent methanol dehydrogenases (MDH) donate electrons from the oxidation of methanol directly through an electron transport chain to O2; this process is coupled chemi-osmotically to the net synthesis of ATP from ADP and Pi. PQQ remains enzyme bound throughout the MDH catalytic cycle and is thought to function as a 2e-/2H+ carrier and to interact directly with the primary alcohol substrate. However, there is little data on the catalytic mechanism of MDH. The overall objective of this proposal is to understand the catalytic mechanism of the PQQ-dependent MDH from Methylbacterium extorquens AM1. Specifically, experiments are proposed here that will define the role of PQQ in the oxidation of the primary alcohol substrate and identify the chemical form of PQQ-bound intermediates in the mechanism. Execution of this program will contribute to our overall understanding of the mechanism of PQQ-dependent enzymes.