Hemoglobin

What is the effect of substrate binding on the T-R equilibrium in allosteric enzymes?

Binding to one active site stabilizes the R state, promoting activity in other sites.

What are the units of the proportionality constant for second-order reactions?

M−1 s−1.

How does the concerted model explain allosteric enzyme behavior?

It posits that enzymes exist in equilibrium between T (tense) and R (relaxed) states.

What is the clinical importance of loss of allosteric control in enzymes?

It can lead to overproduction of metabolites, causing diseases such as gout.

What does the ratio kcat / KM indicate about an enzyme's performance?

It measures catalytic efficiency, considering both catalysis rate and substrate affinity.

How is KM related to substrate concentration at half-maximal velocity?

When V0 = ½ Vmax, then KM = [S].

What is the definition of reaction velocity?

The change in concentration of reactants or products per unit time.

How can reaction velocity be measured in terms of reactant disappearance?

By measuring how much A disappears as a function of time.

How do allosteric enzymes control metabolic pathways differently from Michaelis-Menten enzymes?

Allosteric enzymes exhibit regulatory properties, allowing for complex feedback mechanisms.

Why is it important to measure initial velocity shortly after the reaction starts?

To obtain accurate measurements before substrate concentration diminishes significantly.

What is the significance of determining KM and Vmax values for enzymes?

They are crucial characteristics that define enzyme efficiency and affinity for substrates.

How is the velocity of a first-order reaction related to reactant concentration?

The velocity is directly proportional to the concentration of the reactant.

Who derived the Michaelis-Menten equation and what does it describe?

Leonor Michaelis and Maud Menten; it describes the initial reaction velocity as a function of substrate concentration.

How do allosteric regulators affect the T-R equilibrium?

Inhibitors stabilize the T state, while activators stabilize the R state.

What are the units of the proportionality constant k in first-order reactions?

s−1.

What information can be obtained from the Lineweaver-Burk plot?

It allows the determination of KM and Vmax values through a straight-line relationship.

What characterizes bimolecular or second-order reactions?

They involve two reactant molecules and their rate depends on the concentration of both.

What distinguishes sequential reactions from double-displacement reactions?

Sequential reactions form a ternary complex; double-displacement reactions have a substituted enzyme intermediate.

What is the significance of quaternary structure in allosteric enzymes?

Allosteric enzymes possess multiple active and regulatory sites that enable cooperative behavior.

How is initial velocity (V0) defined in enzyme kinetics?

As the velocity of the reaction measured when product concentration [P] is approximately zero.

How does diffusion affect k1 in the context of enzyme kinetics?

Diffusion limits k1 to rates between 10^8 and 10^9 s−1 M−1.

What kind of relationship does reaction velocity have with substrate concentration in allosteric enzymes?

It displays a sigmoidal relationship, instead of a hyperbolic one found in Michaelis-Menten kinetics.

Why are allosteric enzymes more sensitive to substrate concentration changes than Michaelis-Menten enzymes?

They are more responsive due to their cooperative binding mechanism.

What role does feedback inhibition play in allosteric regulation?

It allows pathway products to inhibit upstream enzymes, maintaining metabolic balance.

How can the regulation of allosteric enzymes be described as complex?

They can be inhibited or activated by various regulatory molecules, influencing multiple pathways.

How does the sequential model account for allosteric effects?

It proposes that subunits change conformation sequentially upon substrate binding.

What does the term KM represent in enzyme kinetics?

The substrate concentration at which the reaction velocity is half of Vmax.

What are the differences between homotropic and heterotropic effects in allosteric regulation?

Homotropic effects involve substrates affecting enzyme activity, while heterotropic effects involve other regulatory molecules.

How does the turnover number (kcat) define enzyme activity?

It indicates the number of substrate molecules converted to product per second.

In what situations can free enzyme concentration be assumed to equal total enzyme concentration?

When substrate concentration [S] is much lower than KM (i.e., [S] << KM).