Polymerization Of Hb Research Articles

Conformational requirements for the polymerization of hemoglobin S: Studies of mixed liganded hybrids

Gelation experiments with artificially formed half-liganded hybrid tetramers of hemoglobin S demonstrate that when either the α chains or the β s chains are fixed in the cyanmet (CNmet) liganded state, gelation occurs upon deoxygenation of the ferrous chains. The minimum concentration of hemoglobin required for gelation is equivalent for both hybrids ( α 2 cnmet β 2 s and α 2 β 2 scnmet ), is considerably higher than the concentration required to gel deoxy-Hb S ( α 2 β 2 s ), and can be restored to the lower minimum gelling point of α 2 β 2 s by reduction of the CNmet chains with dithionite. These results suggest that the most important conformational determinant of the deoxy state for polymerization of Hb S is the quaternary deoxy structure rather than the tertiary structural effect of the ligand state of the α or the β s chains, and are furthermore consistent with the notion that asymmetric deoxy-CNmet hybrid tetramers assume a conformation which resembles, but is not identical to that of deoxyhemoglobin. The results of gelation experiments with mixtures of hemoglobins S and A in which selected chains of one or both hemoglobins are in the CNmet form support the concept that certain non-S hemoglobins may participate in the sickling process by forming hybrid tetramers with Hb S (such as α 2 β a β s ). The conformational requirement for participation of these hybrids in polymers also appears to be a quaternary deoxy-like structure.

The Fine Structure of Sickled Hemoglobin in Situ

Abstract The sickling of susceptible erythrocytes from patients with sickle cell anemia has been related in previous studies to the intracellular precipitation of reduced sickle hemoglobin (Hb S). Though this knowledge has been available for many years, the form assumed by insoluble reduced Hb S in intact sickled cells has not been previously demonstrated. In the present study, glutaraldehyde incubated with susceptible cells at 37 C. was found to promote the sickling phenomenon as well as preserve the structural form assumed by Hb S after polymerization. Sickled erythrocytes were filled with filaments and rods. The severity of erythrocyte distortion was closely related to the amount of Hb S converted to the rod form and the extent of parallel association of the rods. Cytoplasmic organization in cells sickled by reduced oxygen tension or sodium bisulfite prior to aldehyde fixation was identical to that observed in cells exposed to glutaraldehyde alone. The rods formed by polymerization of Hb S in situ are not morphologically identical to microtubules, but their response to physical and chemical agents suggests that the two types of protein polymers are markedly similar.