MOLECULAR ACTIVATION DEACTIVATION OF XANTHINE-OXIDASE IN HUMAN-MILK

Enzymic activity and protein levels of xanthine oxidase were measured in serial samples of breast milk donated by each of 14 mothers, starti ng, in all but two cases, within 7 days following parturition. Enzyme activity varied widely, usually reaching peak values during the first 15 days and falling thereafter, by as much as 98%, to basal levels tha t were subsequently largely maintained. Corresponding changes in xanth ine oxidase protein levels were not observed and, consequently, the sp ecific activity of xanthine oxidase followed the above pattern. The ca pacity of human xanthine oxidase to undergo activation-deactivation cy cles at the molecular level has important implications, not only for i ts role in breast milk, but also for its potential as a source of reac tive oxygen species in other human tissues.