This book summarizes recent advances in post-translational modification reactions and discusses the significance of these reactions to cellular biology. Topics covered include identification and characterization of various types of post-translational modified proteins by ion spray MAS; sulfation and phosporylation of proteins; non-enzymatic glycation under diabetic conditions; amidation carboxymethylation and ADP-ribosylation of proteins, and enzymatic glycosylation of proteins.