Which of the following would not be a reversible post-translational modification?

An enzyme's active site has high affinity for a polar charged substrate. How will methylation of the active site affect the reaction rate of the enzyme?

Histones are proteins that regulate gene expression by binding to DNA and controlling which regions are exposed to be expressed. Histones bind to DNA at a neutral pH via their positively charged lysine residues, but acetylation of histones leads to the dissociation of the DNA-Histone complex. Covalent modification of lysine's ammonium group by acetylation results in an overall _______________ charge of the histone binding region.