Proteins: Post translational modification I am a physicist and trying to understand some protein chemistry for a small project. Basically, amino acids combine to form proteins and after forming the primary structure, some chemical modification may occur, such as phosphorylation or glycosylation (post translational modification). In case of the enzyme carbonic anhydrase a zinc ion is added post-translationally as a cofactor. (The amino acid sequence can be seen here (scroll down to 'sequence' title). 1. Is the attachment of zinc regarded as a type of post-translational modification? 2. When carbonic anhydrase is denatured, is the zinc ion released in the medium? 3. Will the amino acid sequence (primary structure) be changed after denaturation? If yes, are amino acids removed after denaturation, if yes, which? 4. I guess Zinc will be removed after denaturation. Is the remaining structure the primary protein structure?

> 1) Is the attachment of zinc regarded as a type of post-translational modification?

It is not really considered a post-translational modification because the zinc atom is not covalently bound to the protein. Binding to zinc is adsorption.

> 2) When carbonic anhydrase is denatured, is the zinc ion released in the medium?

Yes, but it depends on the extent of denaturation too. Metal ions can be removed using chelating ligands like EDTA, without actually denaturing the protein.

> 3) Will the amino acid sequence (primary structure) be changed after denaturation? If yes, are amino acids removed after denaturation, if yes, which?

Denaturation does not include cleavage of covalent bonds. There won't be change in the amino acid sequence.

> 4) I guess Zinc will be removed after denaturation. Is the remaining structure the primary protein structure?

Yes; just the polypeptide.