For the following experiments you need a similar solution of egg-white as we used for the previous experiments.

Behaviour against other substances

1) Salting-out effect

Required: ammoniumsulphate

Fill a test-tube to 1/4 with egg-white solution and add ammoniumsulphate until the solution is saturated.
Observation?
Now dilute again with aqua dest.
Observation? - Conclusions?


2) Contamination/Protein poison

Required: solutions of copper-II-sulphate and silvernitrate

Give two pipettes of egg-white solution into each of two test-tubes and add a few drops of coppersulphate solution to the first test-tube. To the other one add a few drops of silvernitrate solution.
Observations?
Now dilute similar to experiment 1.
Observations? - Explanations?


3) Precipitation with trichloroethanoic acid

Required: CCl₃COOH

Give two pipettes of egg-white solution into a test-tube and add one spatula of trichloroethanoic acid.
Observations?


4) Denaturation by heat

Heat a test-tube with egg-white solution until coagulation occurs. Try to dissolve the coagulated protein again!


5) Denaturation by cracking disulphide-bridges

Required: cystine; 10% solution of sodiumsulphite; dil. NaOH

Give two pipettes of sodiumsulphite solution into a test-tube and add one spatula of cystine. Make the suspension basic by addition of a few drops of NaOH-solution and heat.
Observation?
Explanation: cystine is a dimeric structure of cysteine. Both are connected by a disulphide bond -S-S- which can be cracked.