Arginine and lysine are distinguished by their identity as the most cationic (basic) amino acids. They are also the target of many post-translational modifications, e.g. acetylation, citrullination, hydroxylation, methylation, ubiquitination. These modifications are catalyzed by a series of enzymes, presumably to enable a tapestry of functionality by a single protein, including regulation of DNA transcription, repair and replication. Besides their functional roles in normal physiological conditions, some of these protein modifications have been recognized as inflammatory triggers and targets of autoimmune reactions. This article is protected by copyright. All rights reserved.