Dehydrogenation

DEHYDROGENATION, the removal of hydrogen from a given compound. According to Wieland (H. Wieland), dehydrogenation lies at the basis of every oxidative process occurring in a living cell. In this process, a water molecule is initially added to the molecule of the oxidizable substance in cases where it is not saturated with hydrogen. The resulting hydrate then loses H, is dehydrogenated, and as a result, an oxidized compound is obtained. Thus, hydration: CH₃CHO + H₂O -> CH₃CH(OH)₂ - H₂ -> CH₃COOH (acid).

According to Wieland, the most important moment of the entire process is precisely the splitting off, the removal of hydrogen from the hydrate. If the hydrogen has separated, it can then easily be captured (accepted) by any compound capable of being reduced. In particular, in the process of respiration, molecular oxygen from the air can serve as such a hydrogen acceptor. Consequently, there is no need for the activation of this oxygen. The role of the cell's oxidative enzymes is reduced to the catalysis of dehydrogenation. Therefore, Wieland believes that there exists only one category of oxidative enzymes—so-called dehydrases. Research by other authors (in particular A. Bach and his students) makes one strongly doubt the correctness of Wieland's position. Molecular oxygen (without preliminary activation) cannot serve as a hydrogen acceptor. In a living cell, there are two groups of oxidative enzymes that are sharply separated by their functions. One of them (oxidases) cannot have any significance in the process of dehydrogenation (as understood by Wieland). They possess the ability to activate oxygen and to accelerate only those processes that proceed at the expense of molecular oxygen. Their role in the living cell is reduced to the oxidation of compounds of the polyphenol type (so-called respiratory chromogens) by gaseous oxygen. In this process, quinone-like substances (respiratory pigments) are formed, which possess the ability to very avidly accept hydrogen. The other group of enzymes (oxidoreductases) accelerates a coupled oxidation-reduction reaction proceeding at the expense of the elements of water. This reaction consists in the fact that the hydroxyl of water goes to the oxidation of one or another cell compound (the oxidizable substance), while the hydrogen of water is accepted by the respiratory pigment, reducing the latter back into a chromogen.