Aminoacyltransferases are acyltransferase enzymes which act upon an amino group. For instance, aminoacyl tRNA synthetases attach an aminoacid through esterification to their corresponding tRNA. The activation of amino acids with aminoacyl-tRNA synthetase requires hydrolysis of ATP to AMP plus PP_i. The aminoacyl-tRNA molecule has close relationships with elongation factors like EF-Tu.