| Popis: |
Molybdenum requiring enzymes have been identified in virtually every species. All molybdoenzymes, with the single exception of nitrogenase, require a molybdopterin cofactor for catalytic activity. Mutations leading to a simultaneous loss of all molybdoenzyme activities have been identified in organisms including, E.coli (1), higher plants such as Nicotiana and Arabidopsis (2,3), as well as Drosophila (4,5), and humans (6). Such mutations identify genes involved in the synthesis and/or activiation of the cofactor. Much of the current interest in MoCF genes stems from the crucial roles of the molybdoenzymes. One example is nitrate reductase,which is the key enzyme in nitrogen assimilation by plants. At least 90% of the total nitrogen assimilated by plants is from the mineral nitrogen, mostly in the form of nitrate (7). A mitochondrial molybdoenzyme, sulfite oxidase (SO) catalyzes the terminal step in the oxidative degradation of sulfur containing amino acids and is responsible for the detoxification of sulfite (8). Complete lack of sulfite oxidase activity leads to a buildup of toxic sulfites which (perhaps combined with a deficiency in sulphates) results in a severely debilitating human genetic defect involving abnormal neurological development. |
