Possible Extension

1.   Try other simple enzymes. Refer to college biochemistry texts for examples.
2.   pH also affects enzymes. Design studies to show the effect of pH on catalase
      and other enzymes.
3.   Have students perform library research and write reports pertaining to enzymes.

Assessing Laboratory Learning
Although you should not penalize students for not obtaining data that ‘‘fit” the
graphs, they should be evaluated on their laboratory technique, ability to work as a
group, and ability to record data.

References
    These activities are modified from those found in:
    Borgford, C., and Summerlin, L. (1988). Chemical activities. Washington:
        American Chemical Society.
    Summerlin, L., Borgford, C., and Ealy, J. (1987). Chemical demonstrations: A
        sourcebook for teachers, Volume 2. Washington: American Chemical Society.

CAUTION: Use appropriate safety guidelines in performing demonstrations.

Demonstration 1: Calcium ions, Rennin, and the Coagulation
of Milk

Purpose
This demonstration illustrates the importance of a metal ion as an enzyme
activator.

Safety
There are no special precautions for this demonstration. Students should be
careful with the warm water.

Materials

Whole milk
Sodium citrate
Rennin (sold in grocery stores as Rennilase or Rennet), available from
biological supply companies
Beaker of warm water

Procedure
Place 15-mL samples of fresh, whole milk in each of two large test-tubes. To one,
add a pinch (match-head size) of sodium citrate, and stir. Add nothing to the
other test-tube. Add a small amount of the enzyme to both test-tubes (about 5
drops of rennilase, or about 1/4 tablet of rennet). Place both test-tubes in a larger
beaker of warm water for three to 5 min. Compare the results.

Remarks
Rennin is an enzyme that converts the soluble milk protein caseinogen into
the insoluble protein paracasein, producing the curd that can be processed
into cheese or other milk products. Calcium ion is required to activate the
enzyme rennin. In this demonstration, calcium ion is removed by precipitating
it as calcium citrate. In the tube containing the sodium citrate, calcium
citrate forms as a precipitate:
Na₃C₆H₅O₇ (aq) + Ca²⁺ (aq) => NaCaC₆H₅O₇ (s) + 2Na⁺ (aq)
 

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