Scientists studying the principles behind oxygen-hemoglobin dissociation have discovered a way to successfully separate hemoglobin tetramers into individual alpha and beta subunits. During an experiment, a solution is created that contains only monomeric beta-hemoglobin subunits under physiologic conditions. If measured, the oxygen dissociation curve of the dissolved beta subunits will most likely resemble which of the following lines?

Question

Scientists studying the principles behind oxygen-hemoglobin dissociation have discovered a way to successfully separate hemoglobin tetramers into individual alpha and beta subunits.  During an experiment, a solution is created that contains only monomeric beta-hemoglobin subunits under physiologic conditions.  If measured, the oxygen dissociation curve of the dissolved beta subunits will most likely resemble which of the following lines?

Quizplus · Accepted Answer

11ec160b_36e7_1d16_9249_21dec3570855_MD0001_00 Hemeproteins such as hemoglobin and myoglobin contain heme groups that are used to reversibly bind oxygen for transportation and storage. Hemoglobin A (the major form of hemoglobin in adults) is a tetramer consisting of 2 alpha and 2 beta chains. Each hemoglobin subunit is associated with a heme moiety, so each hemoglobin molecule has 4 heme groups. After binding to 1 oxygen molecule, the oxygen affinity of other heme molecules increases; this heme-heme interaction is responsible for the characteristic sigmoid shape of the oxygen-hemoglobin dissociation curve. In contrast to hemoglobin, myoglobin is a monomeric protein and the primary oxygen-storing protein in skeletal and cardiac muscle tissue; it is only found in the bloodstream after muscle injury. The partial pressure of oxygen at which 50% of myoglobin molecules are oxygen saturated (P₅₀) is only 1 mm Hg, which is much lower than the P₅₀ of hemoglobin (26 mm Hg). Myoglobin also has only a single heme group and so does not experience heme-heme interactions; therefore, its oxygen-dissociation curve is hyperbolic. The secondary and tertiary structures of myoglobin and the hemoglobin beta subunit are almost identical (the α-subunits are also very similar to myoglobin). Because individual hemoglobin subunits are structurally similar to myoglobin, their oxygen-binding behavior is also similar. That is, if a hemoglobin molecule is dissociated, the individual subunits will have a hyperbolic oxygen-dissociation curve (Choice A). (Choice B) Line B is left-shifted compared to normal hemoglobin A, which could indicate a high oxygen affinity hemoglobin (eg, fetal hemoglobin). Hemoglobin A will also undergo a left shift in the presence of factors such as increased pH, decreased temperature, and decreased 2,3-diphosphoglycerate. (Choice C) Line C depicts the normal oxygen-hemoglobin dissociation curve, with the typical sigmoidal relationship of pO₂ to hemoglobin O₂ saturation. (Choices D and E) Lines D and E are shifted to the right, indicating a low oxygen affinity hemoglobin. Hemoglobin A has low affinity for oxygen under conditions such as decreased pH, increased temperature, and increased 2,3-diphosphoglycerate. Educational objective: The individual subunits of the hemoglobin molecule are structurally analogous to myoglobin. If separated, the monomeric subunits will demonstrate a hyperbolic oxygen-dissociation curve similar to that of myoglobin. __________ References: Myoglobin oxygen dissociation by multiwavelength spectroscopy. (http://www.ncbi.nlm.nih.gov/pubmed/9029202) Configuration of the hemoglobin oxygen dissociation curve demystified: a basic mathematical proof for medical and biological sciences undergraduates. (http://www.ncbi.nlm.nih.gov/pubmed/17562911)

Scientists Studying the Principles Behind Oxygen-Hemoglobin Dissociation Have Discovered a Way