Page 208 - The Manga Guide to Biochemistry

Since the enzymes remain active, the maximum reaction rate Vmax is not affected, but
the Km value will rise, since some of the enzymes accidentally bind to inhibitors. With inhibi-
tors getting in the way, it takes longer for enzymes to bind to substrates, producing the

same result as if a lower substrate concentration was present.

If a competitive inhibitor is added, the slope of the straight line will be greater on a

Lineweaver-Burk reciprocal plot, as shown below. Note that the intersection with the y-axis,

1/Vmax, doesn’t change.

y If the slope Competitive
inhibition
increases and
1 changes
Km

1
Vmax

-1 x
Km

Although the intersection with the y-axis doesn’t change, the intersection with the
x-axis does. This means that if you add an unknown inhibitor to an enzyme reaction, take
measurements, graph the result, and see that 1/Km has increased, you know it’s a competi-
tive inhibitor.

Non-competitive inhibition is when an inhibitor bonds at a part of the enzyme unrelated
to the substrate bonding site to inhibit the enzyme reaction.

Inhibitor

Enzyme

Substrate

The active site is empty, but the
enzyme’s shape is changed by the

bound inhibitor, preventing the
reaction from occurring smoothly.

194 Chapter 4