Oxygen-storing pigmented protein in muscle cells.

• A. Hemoglobin
• B. Ferritin
• C. Myosin
• D. Myoglobin

Answer: (D)

Myoglobin is the oxygen-storing pigmented protein in muscle cells. It is a small, heme-containing protein found in the muscle cytoplasm that binds a single molecule of oxygen. Its role is to act as an oxygen reservoir and to facilitate the diffusion of oxygen from the bloodstream to the mitochondria during muscle activity when oxygen demand rises. Because myoglobin has a higher affinity for oxygen than hemoglobin, it can hold onto O2 and release it where and when muscles need it most, especially under low oxygen conditions. The pigment gives muscle tissue its reddish color, with more myoglobin in oxidative (slow-t-twitch) fibers contributing to their darker appearance. This is distinct from hemoglobin, which carries oxygen in the blood; ferritin, which stores iron, not oxygen; and myosin, which is a motor protein involved in muscle contraction rather than oxygen storage.