Some further evolved GAT enzymes of the invention comprise one or more amino acid residue positions not observed in previously described GAT polypeptides and GAT enzymes, such as, at position 27, a B1, Z1 or A amino acid residue; at position 33, an N or G amino acid residue; at position 46, a B2, Z4, or H amino acid residue; and at position 93, an R amino acid residue; where B1 is an amino acid se