What is the main transport protein responsible for carrying oxygen in the blood?

Hemoglobin is the main transport protein responsible for carrying oxygen in the blood. It is a complex protein found primarily in red blood cells and consists of four subunits, each containing an iron atom that can bind to oxygen molecules. This binding is crucial for the delivery of oxygen from the lungs to various tissues throughout the body, where it is used to produce energy. Hemoglobin not only facilitates oxygen transport but also plays a role in transporting carbon dioxide, a waste product of metabolism, back to the lungs for exhalation.

In contrast, loboglobin and hemocycline are not recognized as oxygen transport proteins in the bloodstream. Loboglobin is not a standard term associated with oxygen transport, and hemocycline does not exist as a known protein in biological systems. Tetracycline is an antibiotic and not related to oxygen transport at all, further indicating its irrelevance in the context of this question. Overall, the unique structure and function of hemoglobin make it the definitive answer regarding oxygen transport in the bloodstream.