Question

Aminotransferases A. usually require \(\alpha\) -ketoglutarate or glutamine as one of the reacting pair. B. catalyze reactions that result in a net use or production of amino acids. C. catalyze irreversible reactions. D. require pyridoxal phosphate as an essential cofactor for the reaction. E. are not able to catalyze transamination reactions with essential amino acids.

Short answer

A) They usually require α-ketoglutarate or glutamine as one of the reacting pair. B) They use up amino acids during the reaction. C) Aminotransferase-catalyzed reactions are irreversible. D) They require pyridoxal phosphate as an essential cofactor. E) They can only catalyze transamination reactions with essential amino acids. Answer: A and D

Step-by-step solution

Identifying the properties of aminotransferases

Aminotransferases catalyze transamination reactions, which helps in the metabolism of amino acids. These enzymes transfer the amino group from an amino acid to an α-keto acid, which results in the formation of a new amino acid. Therefore, let's analyze each statement one by one.

Option A: Reacting pair involvement

Aminotransferases usually require α-ketoglutarate (which acts as an acceptor of the amino group) or glutamine (which acts as a donor of the amino group) as a reacting pair in the transamination reaction. This statement is true.

Option B: Net use or production of amino acids

Since aminotransferases transfers amino groups between amino acids and α-keto acids, they don't use up or produce amino acids in the reaction, but rather transform one amino acid into another. So, this statement is false.

Option C: Irreversible reactions

Aminotransferase-catalyzed reactions are usually reversible as they can both synthesize and degrade amino acids depending on the cellular requirements. Thus, this statement is false.

Option D: Essential cofactor requirements

Aminotransferases do require a cofactor for their catalytic function. This cofactor is pyridoxal phosphate (PLP), which plays a vital role in the transfer of the amino group. This statement is true.

Option E: Essential amino acid reactions

Aminotransferases can catalyze transamination reactions with essential amino acids as well as non-essential amino acids. Essential amino acids are simply the amino acids that must be obtained through diet since our bodies cannot synthesize them. This means that this statement is false.

Conclusion

From the above analysis, we can conclude that options A and D are the correct statements about aminotransferases. They usually require α-ketoglutarate or glutamine as one of the reacting pair and require pyridoxal phosphate as an essential cofactor for the reaction.

Key concepts

α-Ketoglutarate

α-Ketoglutarate is a key organic compound in the Krebs cycle, also known as the citric acid cycle or TCA cycle, which is fundamental to cellular respiration in living organisms. Its paramount role in aminotransferases comes from its ability to accept amino groups during transamination reactions. Thus, it acts as an amino group acceptor, creating a new amino acid while itself becoming glutamate.

As a critical molecule in metabolism, α-ketoglutarate is involved in various biosynthetic pathways. Its presence in a reaction involving aminotransferases ensures the continual supply of amino acids that are essential for the synthesis of proteins. Moreover, α-ketoglutarate's versatility also exhibits its involvement in regulating protein degradation, signaling pathways, and the antioxidant response, marking it as a molecule of significant metabolic importance.

Glutamine

Glutamine, considered a non-essential amino acid under normal physiological conditions, plays an essential role in various metabolic processes. It is not only an amino group donor in transamination reactions facilitated by aminotransferases but also a key nitrogen carrier in the body. In the context of transamination, glutamine can transaminate with α-ketoglutarate, donating its amino group to produce glutamate.

In addition to being a substrate for protein synthesis, glutamine is crucial in maintaining nitrogen balance. It serves as a precursor for the synthesis of nucleotides and other amino acids, making it indispensable for rapidly dividing cells, such as immune cells and intestinal cells. Glutamine also has a special place in clinical nutrition, being used as a supplement in critical care for patients to boost recovery.

Pyridoxal Phosphate

Pyridoxal phosphate (PLP) is the active form of vitamin B6 and serves as a coenzyme in various enzymatic reactions. In the context of aminotransferases, PLP is absolutely essential due to its role as a cofactor in these enzymes' catalytic processes. It binds to the enzyme and forms a Schiff base with the amino acid substrate, which stabilizes carbocation intermediates allowing for the transfer of amino groups.

Its role goes well beyond just aminotransferase reactions; it is involved in over 100 enzyme reactions, mostly with amino acids. These include decarboxylation reactions, deamination, and racemization of amino acids. Pyridoxal phosphate's multifaceted functions indicate its critical importance in amino acid metabolism and the necessity for proper vitamin B6 intake in our diet for maintaining metabolic homeostasis.

Transamination Reactions

Transamination reactions are a cornerstone of nitrogen metabolism in cells and involve the transfer of an amino group from an amino acid to an α-keto acid. These enzymes facilitate a two-way street; they can synthesize amino acids by picking up amino groups from available amino acids and attaching them to α-keto acids, or they can degrade amino acids by removing their amino groups and transferring them to α-ketoglutarate, producing glutamate.

In these reactions, aminotransferases demonstrate incredible specificity for their substrates but also exhibit remarkable flexibility with respect to the number of amino acids with which they can interact. These reactions do not result in a net gain or loss of amino acids but rather contribute to amino acid cycling within the body, emphasizing their sustainable and efficient nature as metabolic processes.