Question

Pb(OAc)2 Test:
Adding Naoh and crystals of Pb(OAc)2 to fish extract, then heated will produce:
What color changes?
What amino acid is detected?

Answer 1

Reduced sulfur test:
Principle:
Proteins containing sulfur (in cysteine and cystine) give a black deposit
of lead sulfide (PbS) when heated with lead acetate in alkaline medium.

Answer 2

Procedure & observation:
− To 1 ml of protein solution in a test tube, add 2 drops of 10% sodium
hydroxide solution and 2 drops of lead acetate.
− Mix well and put in a boiling water bath for few minutes; a black deposit
is formed with albumin, while a slight black turbidity is obtained with
casein due to its lower content of sulfur. Gelatin gives negative result.

http://www.pua.edu.eg/Version2/Courses2/Dentistry%20Courses/Freshmen/Spring/BCM101/Practical/Week%204%20practical%20_Chemistry%20of%20proteins_.pdf