A 55-year-old man presents to the emergency department with shortness of breath and fatigue. He has a history of chronic obstructive pulmonary disease (COPD) and has been using supplemental oxygen at home. Blood gas analysis shows a PaO₂ of 85 mmHg and a normal hemoglobin concentration. Despite adequate oxygenation, his oxygen delivery to tissues appears impaired. You suspect an issue related to hemoglobin’s oxygen-binding properties and cooperative behavior. Which of the following best describes the conformational change in hemoglobin upon oxygen binding?
