This family represents the catalytic subunit of glutamate-cysteine ligase (E.C. 6.3.2.2), also known as gamma-glutamylcysteine synthetase (GCS). This enzyme catalyses the rate limiting step in the biosynthesis of glutathione. The eukaryotic enzyme is a dimer of a heavy chain and a light chain with all the catalytic activity exhibited by the heavy chain (this family).