Question

Effects of Metal ion poisons on enzyme activity

1. Prepare 3 dry testube and place 1ml of alfa amylase into each tube

2. to testube 1 add 3ml distilled water, to testube 2 3ml of lead acetate soln and to testube 3 1% silver nitrate soln.

3. place all tubes in water bath and set at 37C for 15min then remove the tubes at the same time

4. prepare 3 vials and label A -1, B-1,C-1 and put 3ml of 1% starch soln into each vial then add 2 drops of iodine soln then mix

5. transfer 10 drops of soln into vials; tube1 to A-1, tube 2 to B-1 and tube 3 to C-1. incubate at room temp for 10 min while mixing the vial

6. record the color of soln and indicate if digestion took place (with complete digestion colorless, with partial digestion violet or red and with no digestion dark shade of blue).

Question: provide the color of soln or precipitate then rank from 1-3 (with 1 being colorless signifying the greatest digestion)

Testube (1,2,3)

Color of soln...

Rank...

Answer 1

Metal ions like silver and lead bind to the active of enzymes like alpha amylase as the active site amino acids often provide excellent chelation or ligation sites for the ions. By binding to the active site, these ions reduce the activity of the enzyme even when other conditions like pH and temperature are optimal. Therefore, in the absence of metal ions, the enzyme reduces starch completely leaving the resulting solution colourless when treated with iodine while the two other samples containing silver and lead ions poisons the enzymatic activity leaving the starch solution only partially hydrolysed.

Test tube 1 - colourless : 1

Test tube 2 - violet/red : 2

Test tube 3 - violet/red : 2

However, it is to be noted that the level of enzymatic inhibition is greatly dependant on the metal ion concentration relative to that of the enzyme and so if the ion levels are high enough, it results in the complete inhibition of the enzyme giving unreacted starch that gives as deep blue colour with iodine.