Modification of hemoglobin S with dimethyl adipimidate contribution of individual reacted subunits to changes in properties

Abstract

Both chemically modified and cross-linked derivatives were formed when dimethyl adipimidate, an antisickling agent, reacted with hemoglobin S. About 1.3 mol dimethyl adipimidate (DMA) were incorporated into each mol of globin subunit. β s subunits were more reactive towards DMA and participated to a greater extent in cross-linking reactions than did α subunits. Dimethyl adipimidate modification of hemoglobin S caused an increase in oxygen affinity in either the presence or absence of 2,3-diphosphoglyceric acid (DPG), a small decrease in Bohr effect and co-operativity, and a small but significant destabliization of the conformation of deoxyhemoglobin. Hybrids containing either α-modified ( α t β c s or β s-modified ( α c β t s) subunits were used to demonstrate that, in the absence of 2,3-diphosphoglyceric acid, modification of α subunits accounts for the increase in oxygen affinity and change in conformation of deoxyhemoglobin. Modification of β s subunits had little effect on oxygen affinity, although cooperativity and the Bohr effect were slightly decreased. In contrast, the effect of 2,3-diphosphoglyceric acid on oxygen affinity was decreased only in β smodified hybrids ( α c β t s). The solubility of both concentrated and dilute solutions of deoxyhemoglobin S was increased by dimethyl adipimidate. The increase in solubility of dimethyl adipimidate-treated hemoglobin S in 1.9 M phosphate buffer arose from modification of α and β s subunits. Thus the antisickling effect of dimethyl adipimidate can be attributed to the modification of both α and β s subunits.