Use of nitric oxide as a probe for assessing the formation of asymmetrical hemoglobin hybrids. An attempted comparison between alphaNObetaNOalphadeoxybetadeoxy, alpha2NObeta2deoxy, and alpha2deoxybeta2NO hybrids.

It has been recently demonstrated that some nitrosyl hemoglobin derivatives have different optical spectrum according to the nature of their quaternary structure (Cassoly, R. (1974) C. R. Seances Acad. Sci., Paris 278, 1417-1420; Salhany, J. M., Ogawa, S., and Shulman, R. G. (1974) Proc. Natl, Acad. Sci. U.S.A. 71, 3359-3362; Cassoly, R. (1975) J. Mol. Biol. 98, 581-595). This property has been used in order to detect the presence of asymmetrical hybrids alphaNObetaNOalpha'O2beta'O2 in a mixture of the two hemoglobins alpha2NObeta2NO and alpha2'O2beta2'O2. When one changes, by deoxygenation, the conformation of the hybrid, there is a characteristic modification in the optical spectrum of the nitrosyl subunits. Quantitative analysis of this phenomenon shows that asymmetrical alphaNObetaNOalphadeoxybetadeoxy and symmetrical alpha2NObeta2deoxy hybrids have distinct properties. The structure-linked optical transition is different in rate and amplitude; it is faster and larger for the asymmetrical molecule. Carbon monoxide binding kinetics performed in absence of phosphate have also indicated that the allosteric equilibrium is more displaced in favor of the T state for alphaNObetaNOalphadeoxybetadeoxy by comparison with the symmetrical deoxygenated intermediates.