Which protein stores oxygen in muscle tissue?

• A. Myoglobin
• B. Hemoglobin
• C. Tropomyosin
• D. Troponin

Answer: (A)

Oxygen storage inside muscle is carried out by myoglobin, a small, heme-containing protein located in the cytoplasm of muscle fibers. When blood delivers oxygen to muscles, some of it is taken up by myoglobin and kept on reserve near the mitochondria. This allows muscle cells to access oxygen quickly during the start of exercise or when demand spikes, even if blood oxygen levels momentarily lag behind. Myoglobin has a high affinity for oxygen, so it holds onto it until the mitochondria need it for ATP production.

Hemoglobin, by contrast, is the oxygen carrier in red blood cells, transporting oxygen from lungs to tissues throughout the body. Tropomyosin and troponin are regulatory proteins on actin filaments that control muscle contraction in response to calcium; they don’t store oxygen.