Inhibitory effect of histone on the peroxidase activity of the Hp/Hb complex

The human leukocyte nuclear histones can bind to haptoglobin (Hp), and thus interfere with subsequent binding of Hb. The Hp/Hb complex possesses peroxidase activity, but a Hp/histone complex does not. The inhibitory effect of histone molecules depends directly on the Hp and Hb, as well as the histone concentrations. The biological significance of the complex Hp/Hb as a measure of intravascular hemolysis and the interference of histones in this assay is briefly discussed.