Exploring Enzymes:
Lactex Lab
Your Task:
You are a scientist at a company called Pharmex.
Recently a new treatment for lactose intolerance,
Lactex®, has been developed. In order to verify
the activity of Lactex®, the enzyme must be tested
on different milks which contain sugars, to verify
that it only works on lactose. If the enzyme has
additional activities on other sugars, it may not be
approved for use by the FDA. Four samples, each
containing a different sugar, will be tested with
Lactex. Your job is to determine if Lactex® is
specific for the sugar lactose.
Test Solutions:
•
•
•
•
•
Cow’s Milk: Lactose = Glucose-Galactose
Soy Milk: Sucrose = Glucose-Fructose
Maltose = Glucose-Glucose
Rice Milk: Glucose
Water
What are Enzymes?
• Proteins that catalyze (speed up) a
biochemical reaction
– Lower the amount of energy needed to start a
reaction
– Do not get used up as part of the reaction
• Identified by their ‘ase’ Ending
• Enzymes act upon substrates
• Animation
Lactase
The sugar lactose is the substrate for the lactase enzyme:
Given that other sugars have similar chemical structures,
is lactose the only substrate for this enzyme???
Lactose Intolerance
• Lack sufficient lactase enzyme  Inability
to digest lactose
•
-
What causes lactose intolerance?
Genetics
Age
Certain medications, infection
Lactose Intolerance by Region
http://4.bp.blogspot.com/_LH_BweOJx_E/TTmGnSwPwII/AAAAAAAAAGE/jNieRVTLbUQ/s1600/Lactose%2Bintolerance.png
Most mammals normally become lactose intolerant after weaning. Some human populations
have developed lactase persistence (in which lactase production continues into adulthood)
resulting from a mutation that is postulated to have occurred 5,000-10,000 years ago,
coinciding with the rise of cattle domestication. This mutation has allowed almost half of the
world’s population to metabolize lactose without symptoms. This distribution is now thought
to have been caused by recent natural selection favoring lactase persistent individuals in
cultures that rely on on dairy products. (Source: Wikipedia)
Materials
•
•
•
•
•
Cow’s milk - contains lactose
Soy milk - contains sucrose
Rice milk - contains glucose
Maltose
Distilled Water
• Lactex Enzyme Solution – contains lactase
enzyme
• Glucose test strips
Glucose Test Strips
Read results at 30 Seconds. Record in % or
mg/dL.
Data Table
Glucose Presence:
Solution
Before Enzyme
Prediction /
Actual
After Enzyme
Prediction /
Cow Milk (lactose)
/
/
Soy Milk (sucrose)
/
/
Rice Milk (glucose)
/
/
Maltose (optional)
/
/
Distilled Water
/
/
Discussion - What do you think will happen?
Actual
Procedure
C
S
R
W
Cow Milk
(lactose)
Soy Milk
(sucrose)
Rice Milk
(glucose)
Water
Step 1: Test for Glucose:
Record Results in Data Table
Glucose Test Strips
Read results at 30 Seconds. Record in mg/dL.
Procedure
C
S
R
Cow Milk
(lactose)
Soy Milk
(sucrose)
Rice Milk
(glucose)
Lacte
x
W
Water
Step 2: Add 0.5 ml lactase
enzyme to each solution –
swirl and wait 2 minutes
Procedure
C
S
R
Cow Milk
(lactose)
Soy Milk
(sucrose)
Rice Milk
(glucose)
W
Water
Step 3: Test for Glucose again.
Record Results in Data Table
Glucose Test Strips
Read results at 30 Seconds. Record in mg/dL.
Conclusion
Discuss your results with your lab partner,
then as a class.
Is the lactase enzyme specific for the sugar
lactose?
What evidence do you have to support this
conclusion?
Conclusion
• Is the lactase enzyme specific for the sugar
lactose?
– Enzymes are specific for a given substrate.
– Lactose is specific for the lactase sugar.
• If your results do not support this
conclusion, why might this be?
Next Steps
• How does the lactase enzyme function
under different conditions?
– pH
– temperature