Do Proteins Have Phosphorus And Sulfur: 7 Important Facts

All proteins in the human body are composed of amino acids consisting of mainly Carbon, Hydrogen, Oxygen and Nitrogen. Here we are going to learn do Proteins Have Phosphorus and Sulfur: 7 Important Facts in this article.

Most Proteins can contain Phosphorous and sulfur depending upon their amino acid backbone. Sulfur is present in side chain of amino acid Cysteine and Methionine and can be added post-translational to Tyrosine. Phosphate ions are added as post-translational modifications to the amino acids Serine, Tyrosine and Threonine.

Amino acids are the backbone of all proteins. Each amino acid is composed of N-terminal amino group, a C-terminal carboxyl group  and a side chain represented as R (R-CH(NH2)-COOH). Each of the 20 amino acids have a different side chain depending upon which the amino acids are classified. These amino acids are joined by peptide bonds to form the primary structure of all proteins.

Primary structure of protein from Amino acids from Wikimedia

Do all proteins have phosphorus?

Of all the amino acids present in proteins, three amino acids with polar side chains can undergo Phosphorylation. These are Serine, Threonine and Tyrosine. Each of them have an Hydroxyl group (OH) attached to their side chain. Thus these are the only amino acids that can undergo Phosphorylation.

The proteins which have Serine, Threonine and Tyrosine amino acids can only contain phosphorous if these amino acids undergo phosphorylation reaction.

Phosphorylation is a common type of post-translational modification found in biological proteins. 30% of all cellular proteins are modified via phosphorylation and more than one-third of them are Serine phosphorylation and 12% are Threonine phosphorylation and 2% are Tyrosine phosphorylation events. So after a protein is synthesized, depending upon its biological function, these three amino acids in its structure may undergo phosphorylation.

Do proteins need phosphorus?

Phosphorous is added by the process of phosphorylation, which is one of the most important and common post-translational modifications found in proteins. 

Addition of Phosphorous occurs via addition of a Phosphate ion. This phosphorylation is an important regulatory mechanism needed for all cellular functions.

The process of phosphorylation is carried out via specific enzymes called Kinases that attach a phosphate moiety (PO4) by replacing the hydroxyl group of the Serine, Threonine and Tyrosine amino acids. The Phosphate group consists of Phosphorous attached to four oxygen molecules, and is supplied by ATP molecule along with energy. The process is given here. Also in some cases, after phosphorylation, specific enzymes called Phosphatases may remove the Phosphates in order to activate the protein.

do proteins have phosphorus
Protein Phosphorylation mechanism from Wikimedia

Do proteins use phosphorus?

Certain proteins need to be phosphorylated to carry out their normal biological function.

Phosphorylated proteins participate in important metabolic processes like signal transduction, cell division, cellular trafficking.

  • Generally, phosphorylation event acts as a molecular switch and phosphorylation / de-phosphorylation activates/deactivuyhj54ghates enzymes and protein factors. These enzymes, for example, Kinase and Phosphatases have amino acids Serine, Threonine, Tyrosine in their active sites that can add or release the Phosphate ions in order to get functional.
  • Phosphorylation can also facilitate protein-protein interaction that is an important part of signal transduction.
  • Phosphorylation is required for reactions with supply of energy because it requires ATP.

These are few of the uses of Phosphorous in proteins.

Does amino acids have phosphorus?

The only way Phosphorous can be added is by addition of a Phosphate ion by replacing the Hydroxyl group from the side chains of the Polar uncharged amino acids

Of all the 20 essential amino acids, none of them contain Phosphorous in their side chain.

Only three such amino acids contain OH-group, that is, Serine, Threonine, Tyrosine, in case of eukaryotes can undergo the process of addition of phosphorous by replacing the Hydroxyl group. Prokaryotes are said to be able to undergo Histidine phosphorylation as well. Even in a protein, only specific amino acid residues undergo phosphorylation.

Is sulfur found in proteins?

Of all the twenty amino acids, Sulfur is found in the side chain of only two of them, Methionine and Cysteine.

Thus proteins containing the amino acids Methionine and Cysteine, contain sulfur. Apart from that, Sulfur is also added as a post-translational modification in proteins.

 In the case of Sulfation, only Tyrosine is the amino acid whose OH- group in the side chain are replaced  by addition of a Sulfate (SO4) moiety by the action of Sulfosyltransferase enzyme. Sulfation is another important post-translational modification. Also two non-essential amino acids, Homocysteine and Taurine contain sulfur as well  but are not incorporated in proteins.

Is sulfur found in all proteins?

Presence of Methionine, Cysteine and, addition of Sulfate ion in Tyrosine residues are the only ways in which Proteins can contain sulfur.

Hence, almost all proteins contain sulfur because Methionine and Cysteine are very common amino acids found in proteins .

Which proteins contain sulfur?

Any protein with Cysteine and Methionine in their composition will contain Sulfur

About 3-6% of all proteins contain sulfur and only 1% of proteins undergo Tyrosine sulfation.

Also, proteins requiring particular Tyrosine sulfation for their function will undergo addition of sulfur as a post-translational modification.

Why do proteins have sulfur?

Proteins containing sulfur are an important source of nutrition in our body. Also Sulfation of proteins contribute to important cellular and metabolic processes.

Both Cysteine and Methionine containing proteins are important components of our metabolic pathways. Tyrosine sulfation, on the other hand, is an important biochemical process and helps in maintaining protein-protein interaction and signal transduction.

Thus maintaining a constant pool of organic sulfur in body and important cellular processes like maintaining homeostasis, leucocyte rolling, visual response and ligand binding to receptors are the main function sulfur-containing proteins.


Proteins are made up of amino acids which do not have Phosphorous in their backbone, so Phosphorous are added post-translationally via addition of Phosphate ion. Sulfur is present in the side chain of two amino acids Cysteine and Methionine and they are incorporated into proteins and sulfate ions are added to Tyrosine residues. Both these processes are important for normal biological function of the body and maintaining homeostasis.

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