Question

REFLECT AND APPLY The enzyme D-amino acid oxidase has a very high turnover number because/the bemino acids lare perwir tentially toxic. The \(K_{\mathrm{M}}\) for the enzyme is in the range of 1 to \(2 \mathrm{m} M\) for the aromatic amino acids and in the range of 15 to \(20 \mathrm{m} M\) for such amino acids as serine, alanine, and the acidic amino acids. Which of these aminolacids, are the preferredstub-wr strates for the enzyme?

Short answer

Aromatic amino acids are the preferred substrates due to their lower \(K_{\mathrm{M}}\) values.

Step-by-step solution

- Identify the enzyme's function

The enzyme D-amino acid oxidase has a high turnover number, indicating it processes substrates quickly. This property is important because D-amino acids can be toxic.

- Understand the significance of \(K_{\mathrm{M}}\)

\(K_{\mathrm{M}}\) is the Michaelis constant, a measure of the concentration at which the enzyme works at half its maximum rate. A lower \(K_{\mathrm{M}}\) value means the enzyme has a higher affinity for that substrate.

- Compare the \(K_{\mathrm{M}}\) values

Aromatic amino acids have \(K_{\mathrm{M}}\) values of 1 to 2 mM, while serine, alanine, and acidic amino acids have \(K_{\mathrm{M}}\) values of 15 to 20 mM. Lower \(K_{\mathrm{M}}\) values suggest a higher affinity for those substrates.

- Determine the preferred substrates

Since aromatic amino acids have lower \(K_{\mathrm{M}}\) values (1 to 2 mM) compared to serine, alanine, and acidic amino acids (15 to 20 mM), the enzyme D-amino acid oxidase prefers aromatic amino acids as substrates.

Key concepts

Enzyme kinetics

Enzyme kinetics involves studying how enzymes bind to substrates and convert them into products. It is crucial for understanding how enzymes work and their efficiency.
Enzymes accelerate chemical reactions by lowering the activation energy required. This makes reactions take place faster.
Key factors in enzyme kinetics include:

• Enzyme concentration
• Substrate concentration
• Temperature
• pH levels

The enzyme D-amino acid oxidase is known for its high turnover number. This means it processes substrates very quickly.
High turnover is beneficial because it helps in rapidly detoxifying potentially harmful D-amino acids.

Michaelis constant (Km)

The Michaelis constant, denoted as \(K_{\mathrm{M}}\), is a vital parameter in enzyme kinetics.
It represents the substrate concentration at which the enzyme operates at half its maximum rate. In mathematical terms, it is the substrate concentration when the reaction rate is at (1/2) Vmax.
A low \(K_{\mathrm{M}}\) indicates high substrate affinity, meaning the enzyme binds well even at low substrate concentrations.
Conversely, a high \(K_{\mathrm{M}}\) means lower substrate affinity, requiring more substrate to achieve the same rate.
In the context of D-amino acid oxidase, aromatic amino acids have a \(K_{\mathrm{M}}\) value of 1 to 2 mM, indicating higher substrate affinity. Meanwhile, serine, alanine, and acidic amino acids have a \(K_{\mathrm{M}}\) value of 15 to 20 mM, indicating lower affinity.

Amino acid metabolism

Amino acid metabolism consists of various biochemical processes where amino acids are synthesized, degraded, and utilized.
D-amino acid oxidase plays a role in degrading D-amino acids, which can be harmful.
Key steps in amino acid metabolism include:

• Transamination
• Deamination
• Urea cycle

Transamination transfers amino groups and helps in the synthesis of non-essential amino acids.
Deamination removes amino groups to produce ammonia, which gets converted to urea and excreted.
D-amino acid oxidase specifically targets D-amino acids, converting them into keto acids and ammonia. This process prevents toxicity in cells and maintains metabolic balance.

Substrate affinity

Substrate affinity refers to how well an enzyme binds to its substrate. High affinity means the enzyme binds strongly at low substrate concentrations.
The Michaelis-Menten equation can be used to describe this relationship:
\[ v = \frac{V_{max} [S]}{K_{m} + [S]} \]
Where:

• \(v\): Reaction rate
• \(V_{max}\): Maximum rate
• \(K_{m}\): Michaelis constant
• \([S]\): Substrate concentration

For D-amino acid oxidase, aromatic amino acids have lower \(K_{\mathrm{M}}\) values (1 to 2 mM), indicating higher affinity as compared to serine, alanine, and acidic amino acids with \(K_{\mathrm{M}}\) values (15 to 20 mM).
This means D-amino acid oxidase is more effective in breaking down aromatic amino acids, reducing their potential toxicity in the body.