Molecular masking and unmasking of the paramagnetic effect of iron on the proton spin-lattice (T₁) relaxation time in blood and blood clots

Abstract

The contribution of hemolysis, proteolysis and the paramagnetic effect of iron on the proton spin-lattice (T₁) relaxation time in blood was examined. Hemolysis induced by sonication resulted in a significant (10%) increase in the T₁ relaxation time of whole blood. Proteolysis in both sonicated and unsonicated whole blood samples eventually yielded T₁ values which correlated well with the relaxation times of free iron in plasma or water at concentrations comparable to the concentration of iron in whole blood. It is concluded that proteolysis allows the iron atom to express its paramagnetic effect on water relaxation by gradually destroying the hydrophobic nature of the pocket in which iron resides on the hemoglobin molecule. The contribution of various blood components to the T₁ relaxation of whole blood was also studied. The T₁ values for packed erythrocytes, intact whole blood, sonicated whole blood, plasma and serum proved to be significantly different from each other. Serum was found to have a significantly (12%) longer T₁ relaxation time than plasma. Packed clotted blood in vitro showed no change in the T₁ time for at least 13 days while packed erythrocytes showed a shortening of T₁ time after 6–8 days.