Question

A man of Japanese ancestry found himself to be experiencing severe flushing and a very rapid heart rate after consuming one alcoholic beverage. His companion, a Caucasian male, did not have the same symptoms even though he had finished his second drink. These physiological effects are related to the presence of acetaldehyde \(\left(\mathrm{CH}_{3} \mathrm{CH} \mathrm{O}\right)\) generated from the alcohol. Acetaldehyde is normally removed by the reaction of mitochondrial aldehyde dehydrogenase which catalyzes the reaction $$\mathrm{CH}_{3} \mathrm{CHO}+\mathrm{NAD}^{+} \leftrightharpoons \mathrm{CH}_{3} \mathrm{COO}^{-}+\mathrm{NADH}+\mathrm{H}^{+}.$$ Acetaldehyde dehydrogenase is a(n) A. oxidoreductase. B. transferase. C. hydrolase. D. lyase. E. ligase.

Short answer

Answer: Acetaldehyde dehydrogenase belongs to the enzyme category "oxidoreductase".

Step-by-step solution

Identify the enzyme activity in the reaction

Given the reaction: \(\mathrm{CH}_{3}\mathrm{CHO}+\mathrm{NAD}^{+} \leftrightharpoons \mathrm{CH}_{3}\mathrm{COO}^{-}+\mathrm{NADH}+\mathrm{H}^{+}\), it can be seen that acetaldehyde dehydrogenase catalyzes the conversion of acetaldehyde to acetate. In this reaction, the transfer of electrons from acetaldehyde to NAD+ is taking place. When an enzyme is transferring electrons between reactants, this process is a redox reaction.

Match the enzyme activity to the correct enzyme type

Now, let's look at the enzyme types given in the problem: A. Oxidoreductase - These enzymes catalyze oxidation-reduction reactions. B. Transferase - These enzymes catalyze the transfer of functional groups between molecules. C. Hydrolase - These enzymes catalyze the cleavage of molecular bonds by adding water. D. Lyase - These enzymes catalyze the cleavage of molecular bonds without adding water. E. Ligase - These enzymes catalyze the formation of molecular bonds by utilizing an energy source.

Choose the correct enzyme type

As acetaldehyde dehydrogenase is involved in a redox reaction catalyzing the transfer of electrons, it belongs to the enzyme category "oxidoreductase". Therefore, the correct answer is: A. Oxidoreductase

Key concepts

Acetaldehyde Dehydrogenase

Acetaldehyde dehydrogenase is an enzyme that plays a critical role in metabolizing alcohol in the body. After you consume an alcoholic drink, your liver begins to break down the alcohol into a toxic compound called acetaldehyde using another enzyme called alcohol dehydrogenase. It is here that acetaldehyde dehydrogenase takes center stage; its primary job is to convert this harmful acetaldehyde into a less toxic substance called acetate.

This conversion is not just a simple swap. Acetaldehyde dehydrogenase facilitates a complex chemical process that involves an electron transport chain. You can think of it as a relay race where electrons pass from acetaldehyde to an electron acceptor molecule, in this case, NAD+, which is reduced to NADH in the process.

For individuals with a particular genetic variation commonly found in people of East Asian descent, the activity of acetaldehyde dehydrogenase is significantly lower, which results in the accumulation of acetaldehyde. This accumulation can lead to unpleasant symptoms like flushing, which the Japanese man experienced, and a rapid heartbeat.

Oxidoreductase

Enzymes are fascinating biocatalysts that are essential to life, and oxidoreductases form a vital subgroup of enzymes. These enzymes are responsible for catalyzing redox reactions, which involve the transfer of electrons between two molecules.

Oxidoreductases come in various types and are critical in many biological processes, such as cellular respiration and photosynthesis. When you think about oxidoreductases, imagine them as matchmakers, introducing donor and acceptor molecules to each other to facilitate this electron transfer. They effectively manage the flow of energy within cells via these redox reactions.

Acetaldehyde dehydrogenase, as we discussed earlier, is categorized under oxidoreductases due to its role in transferring electrons from acetaldehyde to NAD+, a cofactor that acts as an electron carrier. This activity demonstrates the classical function of an oxidoreductase by altering the oxidation states of both the substrate (acetaldehyde) and the cofactor (NAD+).

Redox Reaction

Redox reactions are the backbone of energy production and transformation in living organisms. The term 'redox' is a fusion of 'reduction' and 'oxidation'. During a redox reaction, one molecule will donate electrons and become oxidized, while the other molecule will accept electrons and become reduced.

In our case with acetaldehyde dehydrogenase, the acetaldehyde molecule is oxidized when it loses electrons, whereas the NAD+ molecule is reduced as it gains electrons. It is this elegant electron dance that helps convert toxic acetaldehyde into acetate, which can then enter into further metabolic processes.

Understanding redox reactions is crucial because they are omnipresent in biochemistry; they contribute to cellular respiration, detoxification, and even the synthesis of DNA. Their importance in biological systems cannot be overstated, as they are central to transforming and managing energy within an organism.

Biochemical Pathways

Biochemical pathways can be thought of as the roads of a city's map within a cell that guide the flow of molecular traffic. These pathways are sequences of chemical reactions that occur within a cell, like the pathway involved in metabolizing alcohol.

The metabolism of alcohol mentioned earlier involves a series of enzymatic steps within specific biochemical pathways. Starting with the conversion of alcohol to acetaldehyde by alcohol dehydrogenase, followed by the conversion of acetaldehyde to acetate by acetaldehyde dehydrogenase—each of these enzymes knows exactly where to go and what to do.

Biochemical pathways can be quite intricate, with multiple enzymes working together to ensure that the products of one reaction become the substrates of another. The comprehensiveness of these pathways ensures that cells can perform a vast array of functions, from breaking down nutrients for energy to assembling new molecules that the organism needs to survive.