Studying the physical – Medical – Biological properties of heme group in red blood cells

1. Introduction One of the functions of blood is oxygen transport. On average, many blood cycles carry about 600 liters of oxygen from the lungs to the tissues thanks to the heme group in red blood cells. Heme is a porphyrin molecule that contains Fe2+ in the center, which is an important component of the globin family such as hemoglobin, myoglobin and neuroglobin that binding and /or transporting of oxygen and play a central role. Most of the applications of heme are based on their optical properties. Therefore, understanding the intrinsic absorption of heme nature is important to the advancement of Medical - Biological technology. This article uses two-level model to study the absorption spectra of the heme group in the deoxyhemoglobin molecule.

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176 JOURNAL OF SCIENCE OF HNUE DOI: 10.18173/2354-1059.2017-0047 Mathematical and Physical Sci. 2017, Vol. 62, Iss. 8, pp. 176-181 This paper is available online at STUDYING THE PHYSICAL – MEDICAL – BIOLOGICAL PROPERTIES OF HEME GROUP IN RED BLOOD CELLS Dinh Thi Thuy 1 , Nguyen Ai Viet 2 , Duong Thi Ha 3 , Nguyen Thi Hanh 1 and Le Xuan Hung 1 1 Thai Binh University of Medicine and Pharmacy 2 Institute of Physics, Vietnam Academy of Science and Technology 3 Thai Nguyen University of Education, Thai Nguyen Abstract. Use two - level model to study the properties of the heme group in myoglobin, hemoglobin, neuroglobin in the globin family. It is important for oxygen transport. When heme absorb oxy, absorption spectra of deoxyhemoglobin have a pick at 555 nm [1], the model gives a good agreement with experiment data. Keywords: Heme, hemoglobin, absorption spectra. 1. Introduction One of the functions of blood is oxygen transport. On average, many blood cycles carry about 600 liters of oxygen from the lungs to the tissues thanks to the heme group in red blood cells. Heme is a porphyrin molecule that contains Fe 2+ in the center, which is an important component of the globin family such as hemoglobin, myoglobin and neuroglobin that binding and /or transporting of oxygen and play a central role. Most of the applications of heme are based on their optical properties. Therefore, understanding the intrinsic absorption of heme nature is important to the advancement of Medical - Biological technology. This article uses two-level model to study the absorption spectra of the heme group in the deoxyhemoglobin molecule. 2. Content 2.1. Materials and methods * Material Heme group in human red blood cells and absorption spectra of deoxyhemoglobin. * Methods - Analytical methods and theoretical synthesis - Use mathematica software to simulate the absorption spectra of deoxyhemoglobin in the Lorentz and Gaussian function. Received August 23, 2017. Accepted September 29, 2017. Contact Dinh Thi Thuy, email: Thuydp.dhy@gmail.com Studying the physical - medical - biological properties of heme group in red blood cells 177 2.2. Results 2.2.1. Structure of heme group in red blood cells Heme is a porphyrin molecule that contains Fe 2+ in the center. Hemes are most commonly recognized as components of hemoglobin, the red pigment in blood, but are also found in a number of other biologically important hemoproteins such as myoglobin, cytochrome, catalase, heme peroxidase, and endothelial nitric oxide synthase. Figure 1. Structure of heme Heme group in myoglobin and hemoglobin is capable of binding oxygen through iron atoms. It also contributes to the red expression of muscles and blood. Each heme group contains an iron atom capable of binding to an oxygen molecule (O2). The heme group of hemoglobin is situated in such a way that it is composed of 4 pyrrole coordinating around an iron ion. In addition, there is a proximal histidine group that is also coordinated the iron group constituting the 5th coordination ligand. In the deoxy form, the iron ion is not completely in the plane of the pyrrole rings, in fact it is about 0.4 angstroms below the plane of the ring. This downward shift is due to the proximal histidine ligand on the bottom of the coordination complex. However, when one of the monomers binds to an oxygen molecule, the iron ion gains a sixth coordination ligand, the oxygen molecule itself, and it pulled up 0.4 angstroms to the plane of the pyrrole rings. This shift upwards also pulls the proximal histidine group up as well. It this movement of the histidine group that contributes to the cooperativity property of hemoglobin. The proximal histidine is located at the interface of the alpha and beta subunits found in hemoglogin (hemoglobin having two identical alpha units and two identical beta units). When the histidine group moves upwards, it forces a conformational change in that interface, which conforms the next monomer to situate itself in a fashion that increases its affinity to another oxygen molecule. As that monomer binds an oxygen molecule, the whole process happens again. It this cascade of events, the iron shifting up upon binding and the histidine moving up as a result, that describes the cooperativity that hemoglobin has between its four monomers and the transition it makes from the T state to the R state[2-6]. 2.2.2. Model physics * Lorentz model We consider a one-dimensional harmonic oscillator with mass m, frequency ω0 > 0 and electric charge q[7]. The forces acting on the oscillator are as follows. The elastic force 2 0'' ' ( )mx m x m x qE t     obeys Hooke’s law. The friction 'fF m x   is proportional to Dinh Thi Thuy, Nguyen Ai Viet, Duong Thi Ha, Nguyen Thi Hanh and Le Xuan Hung 178 velocity and directed in the opposite direction, this allows us to take Γ ≥ 0. Moreover, we assume that the oscillator is driven by a classical time–dependent electric field E(t) which exerts the force ( )qF qE t . The corresponding equation of motion follows immediately from second law of dynamics and is of the form 2 0'' ' ( )mx m x m x qE t     . Equation has solution:          00 2 22 20 0 0 1 2( ) cos sin . 1 12 4 4 s qE x t t t m                          (1) We see that the in-phase term (proportional to cos(ωt), as the driving field) has dispersive character. Its amplitude is     0 0 2 2 0 0 , 2 / 2 d disp d f A           (2) It is sketched by a broken line in the figure 2. Figure 2. Shapes of dispersive (broken line) and absorptive (solid line) curves[7]. On the other hand, the out-of-phase term [proportional to sin(ωt)] is absorptive, and its amplitude is     0 2 2 0 0 / 2 , 2 / 2 abs d f A         (3) It is sketched by a solid line in the figure 2. That is the Lorentz absorption spectrum of a harmonic oscillating atom with frequency ω0 that acts on the external force of the periodic radius ωd. It is found that the Lorentz spectrum is symmetric and has an absorption maximum at position Studying the physical - medical - biological properties of heme group in red blood cells 179 ω = ω0 (the atom does not oscillate independently of the effect of friction). The width of the spectrum is due to the friction between the atom and the surrounding environment. * Two-level model of heme in physics When the protein is in an energy state E1 absorbs a photon with energy ΔE = hf, it moves to the state E2 energy and vice versa if protein is in the state E2 energy state emitting a photon energy ΔE = hf then it will return to the basic E1 energy level (Figure 3). We have: E2 = E1 + hf. Figure 3. Energy diagram of two-state quantum system[8]. Based on the experimental results, the absorption spectrum of deoxyhemoglobin is Lorentz type. The energy diagram of the hemogobin group leads to an idea of using the two-level model to describe physics of heme, in which the protein would be considered as a system with only two quantum states[8]: the iron state in heme attaches to oxygen with energy E1 and the iron state in the heme attaches to the histamine having E2 energy. The state E2 energy is blurred with a width Г '. With empirical results, the distribution of deoxyhemoglobin absorption intensity has a gaussian shape. In this essay we first consider this model for the absorption spectra of Deoxyhemoglobin. Figure 4. Energy diagram of hemoglobin group[8] Use mathematica software to simulate the absorption spectra of deoxyhemoglobin in the Lorentz and Gaussian function with different parameter for to find the fitting parameter as with experimental data. Fitting with Gaussian function:                 2 2 2 exp. 2   xa xf (4) We have: Γ = 11, a = 365 and μ = 555 Fitting with Lorentz function: Dinh Thi Thuy, Nguyen Ai Viet, Duong Thi Ha, Nguyen Thi Hanh and Le Xuan Hung 180        22 cx b xf  (5) We have: b = 4.68, c = 0.6 và η = 555 Figure 5. Absorption intensity of deoxyhemoglobin Experimentally[1] Gaussian theory Lorentz theory Comparing the absorption spectra of deoxyhemoglobin experimentally with the curve of the Lorentz function and the Gaussian function with the above parameters, there is quite a good fit in that the Gaussian function is more suitable than the Lorent function. However, there is still a difference between the experimental and the theoretical curve. The cause of this deviation is due to the fact that the heme binds to oxygen independently but ignores the interactions between the heme with its rest and environment. 3. Conclusions This article gave an overview of the Physical - Medical - Biological properties of the heme group in Red blood cells and constructed a two-level simplified physical model for its optical properties. According to this model, the absorption spectrum of deoxyhemoglobin is generated by the shift between the two energy levels. Using the improved Lorent model, the rescarehers found Lorentz absorption spectra. Compared with the experimental results, the Lorentz curve is similar in form to the empirical curve. This prove that this model is applicable. However, in this study I built the simplest model, so when compared to the experimental results, there was still a difference. The cause of this deviation is that we ignored the interactions between the heme with its rest and environment. This article is about building a simple two-level model to explain the absorption spectrum of deoxyhemoglobin. To develop this research direction we expect to build a more accurate model to explain the absorption spectrum of oxyhemoglobin and oxyneuroglobin. Studying the physical - medical - biological properties of heme group in red blood cells 181 REFERENCE [1] A. Buursma W. G. Zijlstra, 1997. Spectrophotometry of hemoglobin: Absorption spectra of bovine oxyhemoglobin, deoxyhemoglobin, carboxyhemoglobin and methemoglobin. Comp. Biochem. Physiol., 118B(4): 743-749. [2] Bernad S Sebban P Sacquin-Mora S Guittet E Lescop E.Bocahut A, Derrien V., 2013. Heme orientation modulates histidine dissociation and ligand binding kinetics in the hexacoordinated human neuroglobin. J Biol Inorg Chem., 18(1): 111-122. [3] Hanoi Medical University, 2001. Biochemistry. Medical Publishing House, Ha Noi. [4] Ministry of health, 2007. Biochemistry. Medical Publishing House, Ha Noi. [5] Paoli, M., 2002. Structure-function relationships in heme-proteins. DNA Cell Biol. 21(4): 271-280. [6] Milani, M., 2005. Structural bases for heme binding and diatomic ligand recognition in truncated hemoglobins. J Inorg Biochem. 99 (1): 97-109. [7] Stanistaw Kryszewski (2004-2010). Quantum optics. Gdansk. [8] To Thi Thao, 2014. Two level model on absorption spectra of oxyhemoglobin, neuroglobin. IOP Publishing 537.
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