Activity E
LACTASE Inhibition Experiment Materials

  1. LACTASE SOLUTION: Make this up just before lab. Add ten drops of liquid Lactaid® or one crushed tablet of Lactaid® to 30 ml of tap water; swirl to mix Label this flask clearly: Lactase Enzyme
  2. The sugar solutions are all saturated. As only 30 ml will be needed by a total of 5 groups, you do not have to make a lot of it.
    1. Label the four flasks thusly
      1. "S" for sucrose
      2. "G" for galactose (the most expensive of these sugars)
      3. "D" for dextrose (glucose)
      4. "L = Lactose sugar"
    2. Put about 30 ml water into each of the flasks.
    3. Slowly dump in the appropriate sugar, and swirl to dissolve. Add enough sugar so that some will not dissolve and settle to the bottom.
  3. ONPG solution: (this is a slow dissolving substance)
    1. This does not keep; make it up 20 minutes before needing it!
    2. Into a 200 ml beaker add 0.200 gm of ONPG powder.
    3. Using a stirring rod, break up the lumps into as fine a powder as you can get it. This will facilitate dissolving.
    4. Add 25 ml water.
    5. Swirl and swirl and swirl and swirl until all is dissolved.
    6. Apportion out into 8 different small tubes for each group's use. (This is important so that groups will not be able to contaminate each other's ONPG solutions with lactase if they don't follow directions properly!)
  4. Each group will need 10 test-tubes, marking pen and a test-tube rack.
  5. Three separately labelled droppers should be available - AND labelled, AND marked for 1 ml or 2 ml.
    • ENZ (2 ml marking)
    • ONPG (either an unmarked dropper; or a 100 μl micropipetter)
    • Sugars (2 ml marking)
      Warn the students to rinse out the sugar dropper with water between sugars.

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