Haeme binding to albumin and equilibria in the albumin-ferrihaemoglobin and albumin-haemopexin systems

Abstract

• 1. The interaction of albumin with haeme was studied by measuring the absorption spectra in the Soret region. Albumin was confirmed to have one strong binding center besides some weaker ones; from the latters haeme can be removed by ion exchange chromatography on DEAE cellulose thus forming an equimolar haeme-albumin complex,

• 2. Haeme transfer within the ferrihaemoglobin-albumin system was studied using CD spectra measurements in the Soret region. The transfer mechanism was described by the four consecutive reactions:

  $$\text{G}{}_4\text{X}{}_{\mathrm{I}}\text{+}\text{A}\text{=}\text{K}{}_{\mathrm{I}}\text{G}{}_4\text{X}{}_{\mathrm{I-1}}\text{+}\text{AX}$$

  (i = 4.3.2.1). characterized by equilibrium constants K₁ = 0.39; K₂ = 0.22; K₃ = 0.032 and K₄ = 0.15.

• 3. The transfer of haeme in the haeniealbumin-apohaemopexin system was investigated by means of difference absorption spectra in the Soret region. The system can be defined by a simple stechiometrie equation

  $$\text{AX}\text{+}\text{Hx}\text{=}\text{K}\text{A}\text{+}\text{HxX}$$

  characterized by the equilibrium constant K = 75.