text: Due to it being a lesser understood post-translational modification, arginylation and its regulation in vivo still remains largely esoteric. The expression of ATE1 can vary significantly within different tissues, but its levels within these tissues peak at mid-development but begin to decline as an organism ages. It has also been observed that a variety of physiological compounds and drugs are able to affect the incorporation of arginine in vivo, but it is hypothesized that this occurs in a non-specific manner. As such, it has been theorized that inhibitors and activators which regulate ATE1 activity, and therefore arginylation, may exist in vivo.  
  Arginylation's ability to make proteins metabolically unstable, as observed in yeast, makes proteins which have been modified in this way an attractive target for removal. One of the well characterized arginylation regulators is the ubiquitin dependent protein degradation which quickly degrades and removes harmful proteins. This important regulator of arginylation facilitates the specificity of this post-translational modification and efficiently removes proteins which were not meant to be arginylated in vivo.  
  Lastly, an unproven but highly attractive mechanism of regulating arginylation in vivo suggests the use of de-arginylation enzymes which may be able to remove an arginine that has been added post-translationally to proteins. Enzymes such as Aminopeptidase B and Carboxypeptidase B are able to remove arginine from a proteins N-terminus and from side chain carboxyl groups, respectively, but do not specifically target arginylated sites. The proposed de-arginylation enzymes are theorized to act in the same way as the previously mentioned enzymes Aminopeptidase B and Carboxypeptidase B, but would differ in the fact that they specifically target arginylated protein substrates. Although these enzymes have not been discovered as of yet, the search for and discovery of these enzymes is an exciting path for further studies.