Question

The enzyme D-amino acid oxidase has a very high turnover number because the \(\mathrm{p}\) -amino acids are potentially 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 amino acids are the preferred substrates for the enzyme?

Short answer

Aromatic amino acids are the preferred substrates for the enzyme.

Step-by-step solution

Understand the Concept of \(K_M\)

The Michaelis constant, \(K_M\), is a measure of the affinity of an enzyme for its substrate. A lower \(K_M\) value indicates higher affinity because it means that the enzyme can achieve half-maximum velocity at a lower substrate concentration.

Identify \(K_M\) Ranges for Different Amino Acids

The problem provides \(K_M\) values for different amino acids. For aromatic amino acids, \(K_M\) is in the range of 1 to 2 mM. For serine, alanine, and acidic amino acids, \(K_M\) is in the range of 15 to 20 mM.

Compare \(K_M\) Values

Compare the \(K_M\) values for the two groups of amino acids. The aromatic amino acids have a lower \(K_M\) (1 to 2 mM) compared to serine, alanine, and acidic amino acids (15 to 20 mM).

Determine Preferred Substrates

Since a lower \(K_M\) value indicates higher affinity, aromatic amino acids are the preferred substrates for the enzyme D-amino acid oxidase because they fall in the lower \(K_M\) range (1 to 2 mM).

Key concepts

Michaelis constant (K_M)

The Michaelis constant, denoted as \({K_M}\), is a crucial parameter in enzyme kinetics. It represents the substrate concentration at which the reaction rate is at half its maximum. In simpler terms, {K_M} helps us understand how strongly an enzyme binds to its substrate. A low {K_M} value indicates a high binding affinity, meaning the enzyme can operate efficiently even at low substrate concentrations. Conversely, a high {K_M} value suggests a lower affinity, needing higher substrate concentrations for optimal functioning.

Enzyme Kinetics

Enzyme kinetics is the study of how enzymes interact with substrates to catalyze reactions. This field examines the rates of these biochemical reactions and how different factors influence them. Key aspects include understanding how enzyme activity changes with varying substrate concentrations, which is often described by the Michaelis-Menten equation. This equation links the rate of enzyme-mediated reactions with substrate concentration, shedding light on vital parameters like \({V_{max}} \) (maximum velocity) and \({K_M}\).

Amino acids substrate affinity

Substrate affinity refers to how strongly an enzyme binds to a particular substrate. Enzymes are selective, often exhibiting a preference for certain substrates over others. This selectivity is quantified by the Michaelis constant (\({K_M}\)). For D-amino acid oxidase, aromatic amino acids exhibit a lower \({K_M}\) (1 to 2 mM), signifying higher affinity. In contrast, amino acids like serine, alanine, and acidic amino acids have a higher \({K_M}\) (15 to 20 mM), indicating lower affinity. Thus, substrates with lower \({K_M}\) values are preferred for enzymatic reactions due to higher bonding efficiency.

Aromatic Amino Acids

Aromatic amino acids are a unique class of amino acids that include phenylalanine, tyrosine, and tryptophan. These molecules feature aromatic rings, making them distinct in structure and function. Due to their lower Michaelis constant (\({K_M}\)), aromatic amino acids are preferred substrates for the enzyme D-amino acid oxidase. This preference suggests a high binding affinity, allowing the enzyme to work efficiently at lower concentrations. The ability of D-amino acid oxidase to bind these amino acids tightly aids in the rapid detoxification of potentially harmful compounds.

Enzyme Turnover Rate

The turnover rate of an enzyme indicates how quickly it can convert a substrate into a product. It is a crucial metric, especially for enzymes involved in removing toxic substances. For D-amino acid oxidase, the high turnover rate ensures that potentially harmful D-amino acids are rapidly metabolized. This rapid action reduces their toxicity, protecting the organism. A higher turnover rate often correlates with enzymes that have a higher affinity for their substrates, reflected by a lower Michaelis constant (\({K_M}\)). Thus, both high turnover rates and low \({K_M}\) values are indicative of efficient enzymatic processes.