Enzyme Regulation: Allosteric Enzymes and Inhibition

Flashcards covering key concepts from the lecture on enzyme regulation, including allosteric enzymes, various types of enzyme inhibition, and the impact of temperature and pH on enzyme activity.

What equation is used to determine the substrate concentration required to achieve a certain percentage of Vmax?

The Michaelis-Menten equation.

What are the main topics covered in the lecture on enzyme regulation?

Allosteric enzymes, types of enzyme inhibition, and enzyme regulation by temperature and pH.

How do Michaelis-Menten enzymes differ from other enzymes in terms of kinetics?

Michaelis-Menten enzymes follow specific kinetic assumptions, and their activity is primarily driven by substrate concentration, whereas other enzymes (allosteric) do not adhere to these assumptions.

What is the primary role of allosteric enzymes in metabolic pathways?

Allosteric enzymes regulate the flux of biochemicals through metabolic pathways, and their kinetics are more complex than Michaelis-Menten enzymes, allowing for greater cellular regulation not solely driven by substrate concentration.

How is enzyme 1, an allosteric enzyme in a metabolic pathway, regulated by its product F?

Enzyme 1 is inhibited by its product F, shutting down the pathway once enough F has been produced.

What type of curve do allosteric enzymes typically exhibit in a velocity vs. substrate concentration plot?

A sigmoidal-shaped curve, indicating large changes in velocity over a narrow range of substrate concentrations.

What is required for an allosteric enzyme to become active, and what is the mechanism behind this rapid activation?

Allosteric enzymes require a certain threshold substrate concentration (a 'switch') to be reached, after which they quickly become active. This rapid activation is achieved through cooperativity.

What structural feature allows allosteric enzymes to exhibit cooperativity, and how does it work?

Allosteric enzymes possess quaternary structure with multiple substrate binding sites. When one site binds substrate, it changes the binding affinity of the other sites, typically increasing it (T form to R form transition).

How do allosteric regulators influence enzyme activity?

Allosteric regulators bind outside the enzyme’s active site and either activate or inhibit enzyme activity by stabilizing either the T (tense, low affinity) or R (relaxed, high affinity) state of the enzyme.

What are the two main categories of enzyme inhibitors?

Irreversible inhibitors (inactivators) and reversible inhibitors.

What are the three types of reversible enzyme inhibitors?

Competitive, uncompetitive, and noncompetitive inhibitors.

How does a competitive inhibitor affect enzyme kinetics (KM and Vmax)?

A competitive inhibitor changes (increases) the KM but does NOT change the Vmax.

How does an uncompetitive inhibitor affect enzyme kinetics (KM and Vmax)?

An uncompetitive inhibitor influences both the KM and the Vmax (both are decreased), but the ratio of KM/Vmax (slope of a Lineweaver-Burk plot) remains the same.

How does a noncompetitive inhibitor affect enzyme kinetics (KM and Vmax)?

A noncompetitive inhibitor changes (decreases) the Vmax but does NOT change the KM.

Which types of reversible inhibitors can theoretically be overcome with a very high concentration of substrate?

Only competitive inhibition can be overcome with a very high concentration of substrate because the substrate can outcompete the inhibitor for the active site.

How does temperature typically affect enzyme activity?

Enzymes have optimal activity at a specific temperature; activity decreases below and above this optimum, with high temperatures generally causing denaturation and a sharp drop in activity.

What is an example of an organism with enzymes adapted to extreme temperatures?

Thermophilic archaea have enzymes that function optimally at high temperatures, allowing them to thrive in environments like volcanic vents.

How does pH typically affect enzyme activity?

Most enzymes have optimal activity at a neutral pH, but some, like pepsin, are adapted to function optimally in highly acidic environments (e.g., pH 2 in the stomach) due to the charge changes of their ionizable groups.