The reversibility of enzyme reaction is scarcely described in Japanese upper secondary school students’ textbooks.
In the present study, I developed a new experimental method for high school students to show the reversibility of enzyme reaction visually using succinate dehydrogenase. It is well-known that dehydrogenases can use oxidized methylene blue (Mb), which is blue-color, as a hydrogen acceptor and reduced Mb (colorless) as a hydrogen donor. Succinate dehydrogenase catalyzes succinate oxidation (dehydrogenation) and its reverse reaction, fumarate reduction (hydrogenation). The optimum pH of this enzyme is about pH 7 for succinate oxidation and pH 8-9 for fumarate reduction.
The succinate oxidation activity of this enzyme could be detected by decolorization of Mb at pH 7. 4 in an evacuated Thunberg tube and, thereafter, the fumarate reduction activity could be detected by coloring of Mb in the same tube when a NaOH solution was transferred from the subchamber of the tube to the main chamber, changing pH of the reaction mixture to pH 8-9.
This method can be applied to observing the reversible reaction of lactate dehydrogenase. Thus, this simple method would enhance students’ understanding of the reversibility of enzyme reaction.
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