Thermal-induced force release in oxyhemoglobin

Abstract

Oxygen is released to living tissues via conformational changes of hemoglobin from R-state (oxyhemoglobin) to T-state (desoxyhemoglobin). The detailed mechanism of this process is not yet fully understood. We have carried out micromechanical experiments on oxyhemoglobin crystals to determine the behavior of the Young’s modulus and the internal friction for temperatures between 20 °C and 70 °C. We have found that around 49 °C oxyhemoglobin crystal samples undergo a sudden and strong increase of their Young’s modulus, accompanied by a sudden decrease of the internal friction. This sudden mechanical change (and the ensuing force release) takes place in a partially unfolded state and precedes the full denaturation transition at higher temperatures. After this transformation, the hemoglobin crystals have the same mechanical properties as their initial state at room temperatures. We conjecture that it can be relevant for explaining the oxygen-releasing function of native oxyhemoglobin when the temperature is increased, e.g. due to active sport. The effect is specific for the quaternary structure of hemoglobin, and is absent for myoglobin with only one peptide sequence.

Physical mechanism for biopolymers to aggregate and maintain in non-equilibrium states

“…The non-equilibrium behaviors of peptide chains have also been observed in native collagen fibril 69, 70 and oxyhemoglobin crystals 71 . When one increase the temperature of native collagen fibril, the measured curves for Young’s modulus and logarithmic decrement are very different for different rates to increase the temperature, i.e.…”

“…Figure 3 shows that for systems with strong springs to connect neighboring monomers in polymer chains, the speed distribution of monomers in the parallel (along the direction of the spring to connect two neighboring monomers) and perpendicular directions have different effective temperatures and such systems are in non-equilibrium states. The non-equilibrium behaviors of peptide chains have also been observed in native collagen fibril 69 , 70 and oxyhemoglobin crystals 71 . When one increase the temperature of native collagen fibril, the measured curves for Young’s modulus and logarithmic decrement are very different for different rates to increase the temperature, i.e.…”

Can morphological changes of erythrocytes be driven by hemoglobin?

“…Surprisingly, a forcerelease effect was found under heating which is generally supposed to diminish mechanical features of biopolymers. It was already noted in [4][5][6] that 49 • C may indicate on structural changes in hemoglobin, but the important aspect of the force release was noted only in [3]. Such an effect is absent in the thermal response of myoglobin.…”

“…We carried out micromechanical experiments on crystals of horse and human hemoglobin [3]. These experiments show that precisely at 49 • C the hemoglobin releases force [3].…”

“…We carried out micromechanical experiments on crystals of horse and human hemoglobin [3]. These experiments show that precisely at 49 • C the hemoglobin releases force [3]. The main advantage of using biopolymer crystals is that there is a possibility of displaying those motions of the macromolecule that can have only transient character in the solution [1,15].…”