Subunit constitution of electrophoretically purified xanthine dehydrogenase of avian liver.

Chick liver xanthine dehydrogenase was highly purified by preparative polyacrylamide gel electrophoresis at the final step of purification, which allowed removal of another contaminating, xanthine-oxidizing enzyme showing a molecular mass of about 380K daltons. Purified XDH showed a specific activity higher than 2,500 units per mg of protein. On treatment with sodium dodecyl sulfate and 2-mercapto-ethanol, XDH was split into two subunits (named as alpha and beta) of different size in an equimolar ratio. The molecular weights of these subunits were estimated as 155K for alpha and 135K for beta. In the form of sodium dodecyl sulfate-complex, subunit alpha tended to degrade into smaller peptides, whereas subunit beta was relatively stable.