Isolation of cofactor common to molybdenum-containing enzymes: nitrate reductase from lupine bacteroids and xanthine oxidase from milk.

A quantitative method for the anaerobic isolation of a molybdenum cofactor from two molybdenum-containing enzymes, nitrate reductase from the bacteroids of lupine nodules and xanthine oxidase from milk, is described. It was established that the cofactor consists of an aromatic component and a number of amino acid residues bound to it. The structural and catalytic function of the molybdenum cofactor in the enzyme was established.