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 neutrofil granulocytes using affinity chromatography on aminohexyl-divinylsulfonyl-agarose. The protein had an M(r) determined by SDS/PAGE, corresponding to diamine oxidase, but had other properties which indicated that it might be a different protein. A combination of protein chemical techniques, including N-terminal sequencing, identified the protein as lactoferrin, an iron-containing protein with an M(r) of approximately 800000, 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 amines and salt. Alignment of the sequences of diamine oxidase and lactoferrin showed that they are similar, indicating a common ancestry for these two different classes of metallo-oxidases.