[Effect of temperature and binding with copper ions on the motility of spin-labeled oxy- and methemoglobin subunits]

Using the method for separate determination of correlation times of spin-labeled proteins (tau M) and labels (tau R) it has been shown that at temperatures below and about 25 degrees the mobility of oxy Hb subunits is higher than that of met Hb. From 30 degrees on oxy and met Hb show identical flexibility (tau M = 40 ns) in 0.01 M phosphate buffer (pH 7.3) containing 0.15 M NaCl. With a decline in pH from 7.3 to 6.4 the intramolecular mobility of met Hb subunits decreases. In the absence of 0.15 M NaCl at pH 7.3 (5 degrees C) met Hb becomes more flexible (tau M drops from 25 to 16 ns). Complex formation of beta-chains of oxy Hb with one Cu+2 ion at 20 degrees has a negligible bearing on the flexibility of the protein, whereas addition of second ion considerably enhances interaction between the subunits of the tetramer and decreases its flexibility (tau M rises from 17 to 30 ns).