QUATERNARY STRUCTURE DYNAMICS AND CARBON-MONOXIDE BINDING-KINETICS OFHEMOGLOBIN VALENCY HYBRIDS

The kinetics of CO binding and changes in quaternary structure for sym metric valency hybrids of human hemoglobin have been extensively studi ed by laser photolysis techniques. Both alpha(+)beta and alpha beta(+) hybrids were studied with five different ferric ligands, over a broad range of CO concentrations and photolysis levels, After full CO photo lysis, the hybrid tetramers switch extensively and rapidly (<200 mu s) to the T quaternary structure. Both R --> T and T --> R transition ra tes for valency hybrid tetramers with 0 and 1 bound CO have been obtai ned, as well as the CO association rates for alpha and beta subunits i n the R reversible arrow T stales, The results reveal submillisecond R = T interconversion, and, for the first time, the changes in quaterna ry rates and equilibria due to binding a single CO per tetramer have b een resolved. The data also show significant alpha-beta differences in quaternary dynamics and equilibria. The allosteric constants do not v ary with the spin states of the ferric subunits as predicted by the Pe rutz stereochemical model. For the alpha beta(+CN) hybrid the kinetics are heterogeneous and imply partial conversion to a T-like state with very slow (seconds) R reversible arrow T interconversion.