LACTOFERRIN - SIMILARITY TO DIAMINE OXIDASE AND PURIFICATION BY AMINOHEXYL AFFINITY-CHROMATOGRAPHY

A protein reacting with a monoclonal antibody against human placental diamine oxidase was purified from the specific granules of human neutr ofil granulocytes using affinity chromatography on aminohexyl-divinyls ulfonyl-agarose. The protein had an M(r) determined by SDS/PAGE, corre sponding to diamine oxidase, but had other properties which indicated that it might be a different protein. A combination of protein chemica l techniques, including N-terminal sequencing, identified the protein as lactoferrin, an iron-containing protein with an M(r) of approximate ly 80000, a high isoelectric point and ferroxidase activity. Purified commercial lactoferrin was shown to bind to aminohexyl-divinylsulfonyl -agarose, and to be eluted in a heterogenous way from the matrix by am ines and salt. Alignment of the sequences of diamine oxidase and lacto ferrin showed that they are similar, indicating a common ancestry for these two different classes of metallo-oxidases.