What protein is primarily responsible for binding O2 in erythrocytes?

Hemoglobin is the protein primarily responsible for binding oxygen in erythrocytes, or red blood cells. It is a globular protein composed of four subunits, each containing a heme group. These heme groups have iron at their center, which is essential for the reversible binding of oxygen molecules. This structure allows hemoglobin to pick up oxygen in the lungs, where the oxygen concentration is high, and transport it to tissues throughout the body, where oxygen is utilized for cellular respiration.

This efficient transport mechanism is critical for maintaining oxygen supply to all body tissues, contributing to cellular metabolism and energy production. Hemoglobin's affinity for oxygen changes depending on several factors, such as pH and carbon dioxide concentration, allowing for effective delivery of oxygen where it is most needed.

Other proteins listed, such as collagen, myoglobin, and albumin, have different roles in the body. Collagen is primarily involved in providing structural support in tissues, myoglobin serves to store oxygen in muscle tissue, and albumin functions mainly as a carrier protein in the bloodstream, helping to maintain osmotic pressure and transport various substances. None of these proteins have the specialized function that hemoglobin has in binding and transporting oxygen in erythrocytes.