Which of the following is a reversible form of post-translational modification which can activate or deactivate a protein depending on the protein which is being modified?

Compare phosphorylation with other PTMs mentioned: Glycosylation involves adding sugar moieties, which is generally not reversible and affects protein folding and stability. Ubiquitination involves adding ubiquitin molecules, often marking proteins for degradation. Acetylation involves adding an acetyl group, which can affect protein function and gene expression but is not typically reversible in the same way as phosphorylation.

Identify that phosphorylation is unique among these options because it is a reversible modification that can rapidly switch a protein's activity on or off, depending on the presence or absence of the phosphate group.