Immunological characteristics of a peroxidase protein in human neonatal cord serum

Adult serum haptoglobin-hemoglobin complexes exhibit acid-stable peroxidase activity. The haptoglobin level in human neonatal cord sera, however, is reported to be very low. We have isolated a protein from the cord sera of neonates, which has acid-stable peroxidase activity analagous to adult serum haptoglobins-haemoglobin complexes, but does not show any immunological identity to adult serum haptoglobins. It differs from the latter in its molecular size and electrophoretic mobility in agarose and polyacrylamide gels. It is unique to cord sera and it bears immunological identity to human IgG.