Prosthetic group phosphoprotein

Biosynthesis of the polypeptide chain is realised by a complicated process called translation. The basic polypeptide chain is subsequently chemically modified by the so-called posttranslational modifications. During this sequence of events the peptide chain can be cleaved by directed proteolysis, some of the amino acids can be covalently modified (hydroxylated, dehydrogenated, amidated, etc.) or different so-called prosthetic groups such as haem (haemoproteins), phosphate residues (phosphoproteins), metal ions (metal-loproteins) or (oligo)saccharide chains (glycoproteins) can be attached to the molecule by covalent bonds. Naturally, one protein molecule can be modified by more means. 

Conjugated proteins contain, in addition to amino acids, a non-protein moiety termed a prosthetic group. Some important examples of conjugated proteins are glycoproteins, lipoproteins, phosphoproteins and chromoproteins. 

Phosphoproteins, which contain phosphoric acid as the prosthetic group, include the caseins of milk (see p. 406) and phosvitin in egg yolk. 

The presence of non-protein prosthetic groups as in glycoproteins, phosphoproteins, lipoproteins, chromoproteins and nucleoproteins. 

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