RELATIONSHIP BETWEEN TETRAMER-DIMER ASSEMBLY AND THE STABILITY OF HB MALMO (ALPHA-2BETA-297GLN)

The effects of the mutation at the .alpha.1.beta.2 contact in Hb Malmo .**GRAPHIC**. on O2-binding properties, ease of dissociation into dimeric Hb and stability were studied. The P50 value of Hb Malmo in the absence of organic phosphates was 1.9 mmHg, in contrast to 8.8 mm Hg of Hb A. The n-value of Hb Malmo was 1.6. The overall free energy of interaction of O2 with Hb Malmo was about 25% that of Hb A. The Adair constant, K1, of Hb Malmo was about 10-times larger than that of Hb A, but the K4 of Hb Malmo was similar to that of Hb A. The liganded form of Hb Malmo dissociated into dimers more readily than Hb A by gel filtration on Sephadex G-100. Dissociation into dimeric Hb was enhanced in dilute solutions. Increased instability during mechanical agitation of diluted samples was greater for Hb Malmo than for Hb A. The denaturation rate constants of tetramers of the oxyform of Hb A and Hb Malmo were about 20-times greater than those of dimers of these Hb. The instability of Hb Malmo depends on a greater .alpha.1.beta.2 dissociation constant compared with that of Hb A. These findings allow an examination of the role of the intersubunit contact in determining the functional properties and the stability of the Hb-molecule.