Plant molybdoenzymes and their response to stress

Molybdenum-containing enzymes catalyse basic reactions in the nitrogen, sulphur and carbon metabolism. Mo-enzymes contain at their catalytic sites an organometallic structure termed the molybdenum cofactor or Moco. In higher plants, Moco is incorporated into the apoproteins of four enzymes: nitrate reductase (EC 1.6.6.1-3; NR), xanthine dehydrogenase (EC 1.1.1.204; XDH), aldehyde oxidase (EC 1.2.3.1; AO) and sulphite oxidase (EC1.8.3.1; SO). Molybdoenzymes in plants are key enzymes in nitrate assimilation, purine metabolism, hormone biosynthesis, and most probably in sulphite detoxification. They are considered to be involved in stress acclimation processes and, therefore, elucidation of the mechanisms of their response to environmental stress conditions is of agricultural importance for the improvement of plant stress tolerance. Here we would like to give a brief functional and biochemical characteristic of the four plant molybdoenzymes and to focus mainly on their sensitivity to environmental stress factors.