Hemoglobin, deoxy

One interesting piece of equipment developed to measure oxygen content of the blood is produced by the Centre for Biomedical Technology in Australia [41]. It consists of five 1W lasers at wavelengths of 780, 800, 830, 850, and 980 nm and uses a photodiode receiver. It uses the hemoglobin/deoxy-hemoglobin absorbance differences mentioned earlier and throws in the S02 content of the blood for good measure. 

Reactivity. Hemoglobin can exist ia either of two stmctural coaformatioas, corresponding to the oxy (R, relaxed) or deoxy (T, tense) states. The key differences between these two stmctures are that the constrained T state has a much lower oxygen affinity than the R state and the T state has a lower tendency to dissociate into subunits that can be filtered in the kidneys. Therefore, stabilization of the T conformation would be expected to solve both the oxygen affinity and renal excretion problems. 

FIGURE 15.31 Subunit motion in hemoglobin when the molecule goes from the (a) deoxy to the (b) oxy form. (Irving G sj... 

The Oxy and Deoxy Forms of Hemoglobin Represent Two Different Conformational States... 

This reaction is driven to the right in tissues by the high COg concentration the equilibrium shifts the other way in the lungs where [COg] is low. Thus, car-bamylation of the N-termini converts them to anionic functions, which then form salt links with the cationic side chains of Arg al41 that stabilize the deoxy or T state of hemoglobin. 

Matthew, JB Hanania, GIH Gurd, ERN, Electrostatic Effects in Hemoglobin Hydrogen Ion Equilibria in Human Deoxy- and Oxyhemoglobin A, Biochemistry 18, 1919, 1979. 

Hemoglobin Is a large complex protein molecule the atomic model of oxyhemoglobin at 2.8 a resolution has been reported In 1968 by Perutz and coworkers, and a similar model of deoxy-hemoglobin In 1970 (1,2). The molecule Is a spheroid, approx-... 

Many analytical techniques have been used to study deoxy- and oxymyoglobin and hemoglobin and their model compounds. A summary of these techniques, adapted... 

X-ray crystallographic structures of myoglobin and hemoglobin were first completed in 19662 and 19753, respectively. Since then, many other X-ray crystallographic studies of deoxy- and oxy- as well as met-myoglobin and hemoglobin have been carried out.22,24 Additionally, researchers have studied the carbon monoxide bound moieties MbCO and HbCO as well as MbNO. Site-directed mutagenesis of residues near the active sites of Mb and Hb have yielded... 

Hydroxyurea reacts with oxy, deoxy and metHb in vitro to form iron nitrosyl hemoglobin (HbNO) and transfers NO to 2-6% of the iron heme groups [115]. Trapping studies using cyanide and carbon monoxide indicate that hydroxyurea oxidizes both oxy and deoxyHb to metHb and reduces metHb to deoxyHb specifically identifying the reaction of hydroxyurea and metHb as the critical reaction in the formation of HbNO from hydroxyurea [115]. Scheme 7.16 depicts the proposed mechanisms of N O and HbNO formation during the reaction of deoxy and metHb with hydroxyurea. Oxidation of hydroxyurea by metHb produces deoxyHb and the nitroxide radical (25,... 

Oxy- and deoxy-hemoglobins are mainly of interest because they are related to the regional cerebral blood flow (rCBF). The focal change in rCBF determines the activation state. The term activation usually refers to the focal increase in rCBF whereas a decrease is called deactivation [78]. With the dual wavelength approach, one can derive two simultaneous equations to be solved for each of the two chromophore concentration changes. To this end, Equation (4) is split into two parts, separating the contributions from HbO and Hb. Equation (4) is then, rewritten as... 

B. Chance, J. S. Leigh, H. Miyake, D. S. Smith, S. Nioka, R. Greenfield, M. Fi-nander, K. Kaufman, W. Lery, M. Yong, P. Cohn, H. Yoshioka, and R. Boretsky. Comparison of time-resolved and unresolved measurement of deoxy hemoglobin in brain. In Proceedings of National Academy of Science, pages 4971-4975, 1988. 

N. Okui and E. Okada. Wavelength dependence of crosstalk in dual-wavelength measurement of oxy- and deoxy-hemoglobin. Journal of Biomedical Optics, 10(l) 011015-l-011015-8, 2005. 

Kerwin BA, Akers MJ, Apostol I, et al. Acute and long-term stability studies of deoxy hemoglobin and characterization of ascorbate-induced modifications. J Pharm Sci 1999 88 79. 

Colombo et al. (1992) examined the water effect on the cooperativity of hemoglobin. They found that about 60 water molecules are involved in the transition between the oxy and the deoxy conformations of hemoglobin. Unfortunately, this paper does not discuss the solvent effect on the free energies involved in the cooperativity of hemoglobin. 

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