26.2. Amino Acids and Proteins http://www.ck12.org
then undergoes a shift in its conformation to produce the product or products, which are then released from the
enzyme active site.
FIGURE 26.7
Typical enzyme-substrate interaction.Over 1,500 enzymes are known. In order to keep track of all these compounds, a classification system was developed
based on the type of reaction catalyzed by each enzyme. Six broad families of enzymes are defined as follows:
- Oxidoreductase –This type of enzyme moves electrons from one compound to another, usually accompanied
by hydrogen atoms (one proton + one electron). - Transferase –These enzymes transfer functional groups (such as –NH 2 or -PO 4 ) from one molecule to another.
- Hydrolase –A hydrolase splits a molecule into two fragments by using water. The catalyzed reaction is referred
to as a hydrolysis. - Lyase –These enzymes split a molecule into fragments without using water.
- Isomerase –Isomerases catalyze rearrangements of their substrates but do not add or subtract material.
- Ligase –These enzymes catalyze the formation of various covalent bonds between separate molecules.
Hemoglobin
Hemoglobin is a large iron-containing protein that binds to oxygen molecules and transports them around the body.
There are four subunits (separate chains) in the hemoglobin complex –two alpha subunits and two beta subunits.
Each subunit contains one iron ion. Its oxidation state changes back and forth between +2 and +3, depending on
whether it is bound to oxygen.
The yellow subunits are identical in structure, as are the gray subunits. A smaller organic structure called a porphyrin
ring is attached to each protein subunit and contains the iron ion used to bind oxygen.