In enzymology, an alanine—tRNA ligase is an enzyme that catalyzes the chemical reaction ATP + L-alanine + tRNAAla ⇌ {\displaystyle \rightleftharpoons } AMP + diphosphate + L-alanyl-tRNAAlaThe 3 substrates of this enzyme are ATP, L-alanine, and tRNA, whereas its 3 products are AMP, diphosphate, and L-alanyl-tRNA. Wikipedia