Question

Is the enzyme described in each of the following statements a simple enzyme or one that requires a cofactor? a. requires vitamin \(\mathrm{B}_{2}\) (riboflavin) b. its active form is composed of 155 amino acids c. uses \(\mathrm{Cu}^{2+}\) during catalysis

Short answer

a. requires a cofactor, b. simple enzyme, c. requires a cofactor

Step-by-step solution

- Determine if a cofactor is needed for enzyme activity (statement a)

The enzyme requires vitamin \(\text{B}_{2}\) (riboflavin). Vitamins often act as cofactors or coenzymes in enzymatic reactions. Therefore, this enzyme is not a simple enzyme but one that requires a cofactor.

- Identify enzyme type based on amino acids alone (statement b)

The statement specifies that the enzyme's active form is composed of 155 amino acids. There is no mention of additional molecules or ions being required. Therefore, this enzyme is a simple enzyme.

- Determine if a cofactor is needed for catalysis (statement c)

The enzyme uses \(\text{Cu}^{2+}\) during catalysis. Metal ions such as Cu²⁺ function as cofactors in many enzymatic reactions. Thus, this enzyme requires a cofactor.

Key concepts

Simple Enzymes

Simple enzymes are enzymes that do not require any additional molecules or ions to function properly. They are entirely composed of amino acids. These enzymes are fully functional in their active form and capable of catalyzing biochemical reactions without the need for cofactors. In the exercise, the enzyme with an active form composed of 155 amino acids falls into this category since it doesn’t need any additional molecules or ions to perform its function. Simple enzymes are often easier to study because they lack the complexity added by cofactors.

Cofactors

Cofactors are non-protein molecules or ions required for the enzymatic activity of certain enzymes. They assist in various biochemical transformations, helping enzymes to catalyze reactions more efficiently. Cofactors can be divided into two main types:

• Inorganic ions like metal ions (e.g., Cu²⁺, Fe²⁺, Mg²⁺)
• Organic molecules which are often vitamins or derived from vitamins and are called coenzymes (e.g., riboflavin or vitamin B₂)

In the exercise, both the need for vitamin B₂ (riboflavin) and the use of Cu²⁺ during catalysis are indicators that cofactors are needed for those specific enzymes to function.

Enzyme Catalysis

Enzyme catalysis refers to the increase in the rate of a biochemical reaction due to the presence of an enzyme. Enzymes lower the activation energy required for a reaction, allowing it to proceed faster. They achieve this via various mechanisms:

• Enzyme-substrate complex formation: The enzyme binds to the substrate to form a complex, aligning reactive groups and stabilizing transition states.
• Providing an optimal environment: Enzymes create a microenvironment that is favorable for the reaction to occur.
• Participating directly in the reaction: Certain enzyme side chains or cofactors can donate or accept protons or electrons.

This makes enzymes highly efficient and specific catalysts in biological systems.

Amino Acids in Enzymes

Amino acids are the building blocks of enzymes. Each enzyme is a specific sequence of amino acids folded into a unique three-dimensional structure, key to its function.

• Active site: The region where the substrate binds and the reaction occurs. It's typically formed by a few crucial amino acids.
• Structural role: Other amino acids help maintain the enzyme’s overall shape and stability.
• Functional diversity: The variety of side chains in the 20 standard amino acids provides enzymes with a wide range of possible reactions.

In the exercise, the enzyme composed of 155 amino acids does not require additional cofactors, showcasing how amino acids alone can sometimes suffice for functional activity.

Vitamins as Cofactors

Vitamins often serve as cofactors or precursors to coenzymes, vital for many enzymatic reactions. They usually help in transferring functional groups from one molecule to another. Specific examples include:

• Vitamin B₂ (Riboflavin): Functions as a part of flavoproteins, important in redox reactions.
• Vitamin B₁ (Thiamine): Part of the coenzyme thiamine pyrophosphate (TPP), essential in carbohydrate metabolism.
• Vitamin B₆ (Pyridoxine): Becomes pyridoxal phosphate, involved in amino acid metabolism.

In the exercise, the enzyme requiring vitamin B₂ implies that it needs this specific vitamin to function correctly, indicating its role as a cofactor in that enzymatic reaction.