Question

Explain in your own words what the overall catalytic efficiency really compares and what it tells us about our enzyme

Answer 1

Increasing the reaction rate of a chemical reaction allows the reaction to become more efficient, and hence more products are generated at a faster rate. These products then become involved in some other biological pathway that initiates certain functions of the human body. This is known as the catalytic efficiency of enzymes, which, by increasing the rates, results in a more efficient chemical reaction within a biological system.

In order for an enzyme to be active and be energetically favorable to allow a chemical reaction to proceed forward, a substrate must bind to an enzyme's "active site". An active site can be thought of as a lock and the substrate as a key; this is known as the lock and key model. A key (substrate) must be inserted and turned (chemical reaction), then the lock (enzyme) opens (production of products). Note that an enzyme might have more than one active site. Another theory on the active site-substrate relationship is the induced fit theory, which is quite opposite of the lock and key theory (where the active site is seemingly inflexible). In the induced fit theory, the active site of the enzyme is very flexible, and only changes its conformation when the substrate binds to it.

The efficiency of the enzyme can be determined as follows: Michaelis Menton equation

v0 = Vmax[S] / KM+[S]

This equation gives the rate of the reaction at a given substrate concentration, assuming a known V_max, which is the maximum rate the reaction can proceed at, and K_M, the Michaelis constant. However, in a practical application of the Michaelis-Menten, V₀ is often measured, and V_max is observed as a saturation or plateau in a data plot. Because the substrate concentration is known, K_M is usually the calculated value of interest.

For K_M, assume V₀ =V_max/2:

V_max/2 = V_max [S] /K_M + [S]

(K_M + [S]) V_max/2 = V_max [S]

K_M + [S] = V_max / V_max/2

K_M + [S] = 2[S]

K_M = [S]

The Michaelis constant can be thought of as the rate at which the substrate becomes unbound from the enzyme, which can either occur in the events of substrate-enzyme complex becoming the product, or the substrate becomes unbound to the enzyme. K_M can be shown as an equation.

K_M = k_-1 + k₂ / k₁

Where k_-1 is the rate constant at which the substrate becomes unbound to the enzyme, resulting in the dissociation of the enzyme-substrate complex, k₂ is the rate constant where the substrate-enzyme complex disappears and turns into product, and K₁ is the rate constant for the formation of the the substrate-enzyme complex formation. Therefore, K_M can be viewed as the rate of substrate-enzyme complex disappearance divided by the rate of substrate-enzyme complex formation, which is the level at which half of the substrate is bound to the enzyme. K_M is a useful indicator for the presence of an inhibitor because we can look for changes in K_M and compare to our control (biological systems that we know have zero inhibitor presence). K_M is a dependent variable, and its value can change due to many reasons, including the pH level of the system, temperature, or any other condition that might affect a chemical reaction. A small K_M indicates that the substrate has a high affinity for the enzyme.

The Michaelis-Menten equation is most useful in measuring enzyme efficiency if v₀ is plotted against [S].