Hemoglobin Binding by Enzymatic Fragments of Haptoglobin

Two fragments, P 1 and P 2 , which were obtained by digestion of haptoglobin by plasmin remained associated in neutral and alkaline buffers, although the electrophoretic and ultracentrifugal behavior of the complex was significantly different from that of native haptoglobin. The P 1 –P 2 complex bound hemoglobin yielding a product indistinguishable at neutral pH from the normal haptoglobin–hemoglobin complex. P 2 had no hemoglobin-binding property. There appears to be a weak interaction between Hb and P 1 as shown by lowered electrophoretic mobility of P 1 in presence of hemoglobin. However, no evidence for a stable complex between P 1 and hemoglobin was obtained.