Concepts of Equilibrium and Steady State
The key to understand catalytic action of an enzyme is the study of reaction velocities and not equilibria. Nevertheless, equilibrium and steady state are two important states of any dynamic system. Both have much relevance to the understanding of enzyme
- PDF / 488,989 Bytes
- 10 Pages / 439.37 x 666.142 pts Page_size
- 98 Downloads / 216 Views
10
The key to understand catalytic action of an enzyme is the study of reaction velocities and not equilibria. Nevertheless, equilibrium and steady state are two important states of any dynamic system. Both have much relevance to the understanding of enzyme mechanisms and hence metabolism. This chapter will elaborate on these concepts. There are many analogies/models to describe these states which include ponds and rivers. We will look at two simple setups to understand what is meant by equilibrium and steady state, before going into details. Imagine two beakers connected via a stopcock. Suppose the stopcock is kept closed and water is filled into one of the beakers. What will happen if the stopcock is opened now? Water will move into the second beaker until the levels in the two beakers are the same (Fig. 10.1). Once the two water levels become equal, there is no net flow of water, and the system as a whole becomes stable (and attains equilibrium). While water molecules continue to diffuse from one beaker into the other – the water level in the two beakers remains same. This is an example of dynamic equilibrium. What happens if the stopcock is now closed? The water level on the two sides remains the same, but there is no free exchange of water molecules across the two beakers. This stable state is an example of static equilibrium. We can distinguish between the static and the dynamic equilibrium by a simple test. A dye introduced in any one beaker will diffuse into the other over time only in the case of dynamic equilibrium. This two-beaker setup is an excellent analogy to “glucose ⇄ fructose” isomerization. Equilibrium mixture of glucose and fructose defines a static equilibrium, as no interconversion occurs due to the prevailing activation energy barrier. Addition of glucose isomerase (enzyme catalyzing this interconversion, equivalent to opening the stopcock and open a path to mix the two compartments!) makes it a dynamic equilibrium. Let us now consider another situation. Suppose we have a beaker fitted with an inlet and an outlet for water as shown (Fig. 10.1). We start filling the beaker by letting water in (through the inlet) at a constant rate. Initially water drains out
# Springer Nature Singapore Pte Ltd. 2018 N. S. Punekar, ENZYMES: Catalysis, Kinetics and Mechanisms, https://doi.org/10.1007/978-981-13-0785-0_10
97
98
10
Concepts of Equilibrium and Steady State
Steady state
Equilibrium Inflow
Inflow>Outflow Level
steady state
Inflow=Outflow Outflow>Inflow
Outflow
Fig. 10.1 Equilibrium and steady state. When the stopcock is opened, water flows into the empty beaker until the two levels become equal – equilibrium is attained (left panel). Water level is maintained as long as the inflow equals the outflow – steady state (right panel)
(through the outlet) more slowly than it enters because of lower water level (and lower hydrostatic pressure). However, this will cause water level to rise in the beaker – generate more pressure – consequently water will drain more quickly. When the inflow of water becom
Data Loading...
