How oxygen is converted into usable energy is a key function in the human body. A pioneer in this field of cellular respiration was Axel Hugo Theodor Theorell, born in Sweden on this date in 1903. Theorell used his imagination and technical skills to isolate and purify peroxidases and cytochromes, two essential enzymes that aid the biochemical reactions the body produces to convert oxygen into energy. For this work, Theorell was awarded the 1955 Nobel Prize for physiology or medicine.

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