What substance is formed when hemoglobin in the red blood cells picks up oxygen lungs?

When hemoglobin in the red blood cells picks up oxygen in the lungs, it forms a compound called oxyhemoglobin. Oxyhemoglobin is a bright red, oxygenated form of hemoglobin that transports oxygen from the lungs to the tissues. When oxyhemoglobin reaches the tissues, it releases oxygen into the cells and becomes deoxyhemoglobin, which is a dark red, deoxygenated form of hemoglobin. Deoxyhemoglobin then carries carbon dioxide from the tissues back to the lungs, where it is released and the hemoglobin is re-oxygenated.