molybdenum

Symbol: Mo. A metal element, atomic number 42, atomic weight 95.94, needed (under certain conditions) in trace amounts for plant growth. It is involved in nitrate reduction being a part of the flavoprotein enzyme nitrate reductase. Plants absorbing nitrogen as ammonium ions do not need molybdenum. The nitrogenase system involved in nitrogen fixation also requires molybdenum since one of the two proteins forming the nitrogenase complex is a molybdenum-iron-sulphur protein.