Alteration of redox stability of hemoglobins A and S by biological buffers

Several organic and inorganic buffers, including Hepes, Tris and potassium phosphate, are often used for the maintenance of pH in hemoglobin solution work. It has often been assumed these buffers do not significantly affect the solution stability of these proteins. This investigation has focused on the effect these buffers have on the redox stability of the heme-iron, [Fe+2-->Fe+3], of hemoglobins A and sickle cell S (beta 6 glu-->val) over extended periods of time. Initial results indicate that: 1) the use of different buffers under similar ionic strength conditions at pH 7.0 affect conformational changes that produce substantial differences in redox stability between Hb A and Hb S; 2) spectral analysis of these hemoglobins in the visible region (700-500 nm) at 37 degrees C for extended periods of time indicated that a slower rate of autoxidation is observed with a Hepes buffered system over a wide ionic strength range than for either Tris or potassium phosphate buffers; 3) Hb S autoxidized at a faster rate in the presence of each of these buffers than Hb A; and 4) in contrast to Hb A, Hb S showed extensive hemichrome formation after 15 hr in the presence of potassium phosphate buffer.