Multiple endogenous amino acids can serve as potential conjugation sites. However, to achieve more precisely controlled site-directed conjugations and subsequently a narrower distribution of drug-to-antibody ratio (DAR), special moieties with unique conjugation chemistries are engineered into antibody sequences in antibody design services. One downside in using the endogenous amino acids for ADC development is a heavily dispersed DAR conjugation caused by the non-uniform distribution of the conjugation sites, especially in the case of Lysine-based conjugations. https://www.creative-biolabs.com/adc/antibody-design-and-conjugation.htm