Pharmacokinetic actions are mediated through the hepatic and gut drug-metabolizing system known as the cytochrome P540 (CYP) enzyme system. For this discussion, you will be assigned one of the following enzyme topics.
CYP 3A4 enzyme
Steps to Take
Each person will receive one enzyme topic.
Use the learning materials and readings below to distill pertinent information regarding your topic.
Answer the questions as they pertain to the enzyme you were assigned. Include at least two references other than Stahl in your answers.
What is your enzyme?
Why is it important?
What does it do in the human body?
What are the common medications that inhibit the enzyme, including any substrates?
What are the important medication restrictions regarding this enzyme?
(rennin), meat (papain), and starch products (amylase).
Experiment 1: Enzymes in Food
(Table – 2 pts)
1. What were your controls for this experiment? What did they demonstrate? Why was saliva included in this experiment? (2 pts)
This experiment is looking for the presence of the enzyme amylase. A positive control would indicate the presence of amylase and so should be something that is KNOWN to contain amylase. A negative control
would indicate no amylase, so should be a substance KNOWN to not
contain amylase. As written, the positive control would be the ginger
root because it is known to contain amylase. The presence of amylase is indirectly
tested for by testing for the presence of starch with an IKI solution.
Amylase breaks down starch into its monomers of the simple sugar
glucose, so if amylase is present, there would be no starch because it
would all be converted to sugars. If amylase is present on the paper
towel it would break down the starch. IKI is yellow, but turns
blue/black in the presence of starch. Once tested with IKI, a yellow color would result indicating no starch.
The negative control will vary by student, but should be a substance known to NOT contain amylase. One example of a negative control in this experiment is water because there is no amylase in water. When you add IKI to water, it does not change color.
Saliva is included in this experiment because saliva contains
amylase. Therefore, the amylase should break down the starch in the
starch solution, causing the IKI to turn yellow/brown upon exposure
(indicating no starch left after the amylase has broken it down
to glucose.) This could also be considered a positive control because we
know amylase is present.
2. What is the function of amylase? What does amylase do to starch? (2 pts)
Amylase is an enzyme that breaks down starch into simple sugars. It is used for digestive purposes in humans.
3. Which of the foods that you tested contained amylase? Which did not? What experimental evidence supports your claim? (2 pts)
Answers will vary by the food products selected. If the IKI was
yellow, that meant no starch was present and so amylase has broken it
down to sugars. If the IKI turned blue/black, then starch is present, so
amylase is not.
4. Saliva does not contain amylase until babies are two months
old. How could this affect an infant’s digestive requirements? (2 pts)
Amylase is required to break down starch in foods like cereal.
Babies can’t digest cereal or other starch containing foods until their
bodies start producing amylase.
5. There is another digestive enzyme (other than salivary
amylase) that is secreted by the salivary glands. Research to determine
what this enzyme is called and identify it. What substrate does it act
on? Where in the body does it become activated, and why? (2 pts)
The salivary glands offer many different digestive enzymes. One example is lysozyme. Also known as muramidase,
this enzyme provides a general antiseptic to kill some of the bacteria
which enters the mouth with food. Specifically, it has been found to
provide a defense against Gram-positive bacteria such as Bacillus and Streptococcus.
It is also found in other body fluids such as tears or milk, and is
considered to be part of the innate immune system. NOTE: the question
asked for salivary enzymes.
Substance Resulting Color Presence of Starch?
6. Digestive enzymes in the gut include proteases, which digest
proteins. Why don’t these enzymes digest the stomach and small
intestine, which are partially composed of protein? (2 pts)
The mucosal lining of the digestive tract contains protease inhibitors,
preventing the enzymes from digesting the stomach intestines.
Furthermore, the coiled structure of the proteins making up the organs
hide the cleavage site. Only when proteins are denatured (cooked or in
high pH) do their cleavage sites reveal themselves so the enzyme can
Experiment 2: Effect of Temperature on Enzyme Activity
(Table – 2 pts)
1. What reaction is being catalyzed in this experiment? (2 pts)
2 H2O2 –> 2 H2O + O2
2. What is the enzyme in this experiment? What is the substrate? (2 pts)
Catalase is the enzyme, found in the yeast. (Yeast is a living
organism that produces the enzyme catalase. Enzymes are proteins, so
connecting with the lecture topic on gene expression–a segment of DNA
in the yeast contains the base pairs to make an mRNA with the codons
that would indicate the correct amino acids to be placed in the right
order to make the specific protein, catalase.)
The substrate it binds with is hydrogen peroxide.
3. What is the independent variable in this experiment? What is the dependent variable? (2 pts)
The independent variable is the different temperature. The dependent variable is enzyme activity
which is measured indirectly by the balloon circumference which is
dictated by the amount of gas (oxygen) produced by the yeast.
4. How does the temperature affect enzyme function? Use evidence from your data to support your answer. (2 pts)
The enzyme function increases as temperature increases.
The yeast exposed to the boiling water bath produced the most gas while
the yeast exposed to the ice bath/refrigerator produced the least amount
Tube Temperature (°C) Balloon
5. Draw a graph of balloon diameter vs. temperature. What is the correlation? (2 pts)
The graph will show the correlation that as temperature
increases, balloon circumference increases. This reaction doesn’t show
it, but most enzymes have a temperature-activity curve that looks like a
parabola – activity increases up to a certain temperature, but at
higher temperatures the enzyme begins to break down (denature) and
activity plateaus and then decreases.
6. Is there a negative control in this experiment? If yes,
identify the control. If no, suggest how you could revise the experiment
to include a negative control. (2 pts)
There is no negative control in this experiment. To
include a negative control for this experiment an additional test tube
with hydrogen peroxide, but no yeast (enzyme) could be included. If no
yeast (enzyme) is present, then no reaction should occur and the balloon
should not inflate.
7. In general, how would an increase in substrate alter enzyme activity? Draw a graph to illustrate this relationship. (2 pts)
Generally speaking, an increase in substrate alters enzyme
activity similar to the way an increase in temperature alters enzyme
activity. An increase in substrate will increase enzyme activity until a
saturation point has been met; at which point, enzyme activity will
plateau and eventually decrease. The graph for this would look similar
to the graph provided in Question 5.
8. Design an experiment to determine the optimal temperature for
enzyme function, complete with controls. Where would you find the
enzymes for this experiment? What substrate would you use? (4 pts)
Answers will vary, but the experiment should include all the
necessary steps to isolate one variable and include a control(s). You
should have indicated what the independent, dependent, and controlled
variables, and what you would use as a control.