BIOLOGICAL TRACE ELEMENT RESEARCH 2, 221-227 (1980) Superoxide Dismutase Isoenzymes in Bovine and Human Milk CARL L. KEEN, BO L6NNERDAL,THEODOREN. STEIN, AND LUCILLE S. HURLEY* Department of Nutrition, University of California, Davis, California 95616 Received June 2, 1980; Accepted June 20, 1980 Abstract The presence of superoxide dismutase in bovine and human milk was investigated by ultrafiltration, gel filtration, and isoelectric focusing. Conclusive evidence for the presence of this enzyme in both milks is presented. The molecular weight of the enzyme was estimated by gel filtration on Sephadex G-100 to be 30,000, which is consistent with reported values for the copper, zinc form of superoxide dismutase. In addition, enzyme activity was inhibited by cyanide, thus eliminating the possibility that the enzyme was present in the manganese form. Several isoenzymes were detected by isoelectric focusing in polyacrylamide gel, and the isoenzyme pattern in bovine milk was the same as that found for bovine plasma, suggesting that milk superoxide dismutase originates from plasma. It may be that the presence of copper, zinc superoxide dismutase in milk is important for the maintenance of its oxidative stability. Index Entries: Superoxide dismutase, in bovine and human milk; milk, superoxide dismutase in bovine and human; plasma, and superoxide dismutase; isoelectric focusing, of superoxide dismutase; gel filtration, of superoxide dismutase; ultrafiltration, of superoxide dismutase; copper, zinc superoxide dismutase, in milk. 9 1980 The Humana Press Inc. All rights of any nature whatsoever reserved. 0 ! 63 -4984/80/0600A)221 $02.00 221