The rates of enzymatic reaction and the
affinity enzymes have for their substrates
are important concepts to understand.
I will deal with these topics in the first part
of this presentation covering data analysis.
I will also talk about
allosterism and the affect it has
on enzymes and their catalysis.
Next I will talk about substrate binding and how that
can happen in different mechanisms within enzymes.
And last I will talk about the way that we classify enzymes
and understand reactions in a very much broad sense.
Okay under Michaelis-Menten Kinetics, we
learned that it's important for us to study
enzymatic reactions or the conditions where
our study states. That is we have relatively
constant amounts of ES complex.
Under Michaelis-Menten Kinetics, the equation on the top
applies and this equation tells us some important things
that we are going to learn in this lecture.
Now Vo that is the velocity of a reaction is equal to Vmax
and that's something that we will discuss in a moment,
times the concentration of substrate
divided by another quantity called Km, that we will
discuss, plus the concentration of substrate.
So we have learned two terms here that are
gonna become important for us to understand
and that's Vmax, the maximum
velocity of a reaction and Km
which is a quantity that allows
us to measure the affinity
that an enzyme has for its substrate.
Well, first let's start with Vmax. With Vmax, it's important
to understand what it is, and
why it is and how that happens.
We saw when we plotted Vo versus
the concentration of sustrate below,
that, we saw that the curve
grew and then it leveled off.
And the reason it levels off
is due to the way that enzyme work and the
way that they interact with substrates.
Instead of an enzymatic reaction
going and staying linear
with increasing concentrations
of substrate, what happens is
enzymes get saturated with substrate.
Saturation of substrate means that the
enzyme binds almost constantly bound
substrate, meaning that we have
almost everything in the ES complex.
So at very high substrate concentrations
the enzyme is continually releasing product.
And over time if we add more and more substrate
we exceed the capacity of the
enzyme to bind more substrate.
So under saturating conditions of substrate,
the enzyme is no longer able to stay linear,
and it flattens off. So we
see this hyperbolic plot.
Now an example might be a factory that is making products.
A factory that's making products will have a lot of workers.
And those workers are working on something but if
they don't have enough materials to make product,
then the workers are gonna be standing around for fair amount
of time waiting for material so they can make product.
On the other hand we could imagine that if we
have those same workers working and they have
all the materials they
need to make products,
they are gonna turn out a
certain number of products per day.
If we increase the amount of materials but
we don't increase the number of workers
we are not gonna change that maximum amount they are going
to get. So we see the same thing happening in the real world
that we see happening with enzymatic reactions.
If we want to the increase the amount of
product we have to get more workers,
perhaps get another factory
in order to make more product.
Now enzymes that don't follow Michaelis-Menten
Kinetics, and there are some,
include those that bind
Now in another presentation I talked
about how hemoglobin binds to oxygen cooperatively.
And that means that the binding of one
substrate is affecting the binding of others.
So when this happens, and of course this
only happens for multisubunit proteins,
when this happens, when the binding
of one affects the others,
then of course we are going to see
a change in the velocity; because,
that's going to change the actual
binding conditions of the enzyme.
When we have those things happen we can tell
them pretty easily; because, what we will get
is an "S" shape curve for the V versus S plot,
very much like what we saw with
the hemoglobin binding to oxygen.