Radical enzymes for the biosynthesis of tetrapyrroles

在像血红素和叶绿素这样的四个吡咯的生物合成过程中，共比例比色原III被两个结构上不相关的酶脱羧基。氧敏感的共聚比色原III氧化酶hemn使用[4Fe-4S]-簇和S-腺苷-L-蛋氨酸形成催化所需的底物自由基。氧依赖的hemF使用组氨酸配位的锰来进行相同的活动。对于氯化血红素，天然的电子供体(S)和受体(S)将被确定。Fe-S团簇的氧化还原行为和底物自由基的位置(S)将用光谱方法确定。酶促S-腺苷-L-蛋氨酸结合和利用的性质将被阐明。对于HmF，缺失的锰配体将被识别。将分析锰与氧和底物反应过程中氧化态和金属配位的变化。潜在的酶和底物自由基参与催化将被证明。对于两种酶的识别都很重要的四聚吡咯底物的取代基将使用合成类似物进行评估。最后，为了了解结构-功能关系，必须使用底物类似物的厌氧结晶和X射线分析来阐明这两种酶的原子结构。

During the biosynthesis of tetrapyrroles like hemes and chlorophylls coproporpyhrinogen III is decarboxylated by two structurally not related enzymes. The oxygen-sensitive coproporpyhrinogen III oxidase HemN uses a [4Fe-4S]-cluster and S-adenosyl-L-methionine to form a substrate radical required for catalysis. The oxygen-dependent HemF uses histidine-coordinated manganese for the same activity. For HemN the natural electron donor(s) and acceptor(s) will be identifed. The redox behavior of the Fe-S-cluster and the location(s) of the substrate radical will be determined spectroscopically. The nature of enzymatic S-adenosyl-L-methionine binding and utilization will be clarified. For HemF missing manganese ligands will be identified. Changes in oxidation state and metal coordination during the reaction of manganese with oxygen and substrate will be analyzed. Potential enzyme and substrate radicals involved in catalysis will be demonstrated. Substituents of the tetrapyrrolic substrate important for the recognition by both enzymes will be evaluated using synthetic analogs. Finally, to understand structure-function relationships the atomic structure of both enzymes must be elucidated using anaerobic crystallisation with substrate analogs and X-ray analysis.