The sulfur-containing test for proteins, which is known as the lead acetate test, is used to detect the presence of sulfur within a protein. Sulfur is commonly found in methionine, cysteine, homocysteine and taurine.
To carry out this test, the sulfur-containing protein is first boiled with sodium hydroxide. This reaction converts some of the sufhur in the protein to sodium sulfide. The sodium sulfide is then detected by a solution of sodium plumbate that causes lead sulfide to be precipitated from the alkaline solution.
Sulfur gives some interesting properties to the proteins in which it is found. Although it belongs to the same group as oxygen in the periodic table, it is much less electronegative than oxygen. Because cysteine contains sulfur, it is able to make disulfide bonds easily; this allows it to play a crucial role in protein structure and protein-folding pathways.
Methionine, as another sulfur-containing amino acid, is very important in the body. It reduces the deposit of fat in the liver, helps with creating cartilage and helps with tissue repair. It is also able to help strengthen the structure of hair and nails. It is therefore integral to good health to have these sulfur-containing proteins in the diet.