Significantly, compared to all previously reported single-mutants that enhance the T/H ratio in TxAbf 21,66-68 , H240F/N display the highest transglycosylation yields combined with noticeably greater regioselectivity (Table ). Thus, we combined this mutation with the N216W one, that favours higher regioselectivity towards the (1→2)-linkage of α-L-arabinofuranosyl moieties to the non-reducing terminal D-xylopyranosyl of xylotriose as acceptor (i.e. A 2 XX) . While both transglycosylation activity (SAT, Table ) and yield (62 compared to 82% for H240F) remained relatively high, the reaction was almost completely regioselective (Table and Fig. ). Conveniently, available structural data and the considerable corpus of knowledge related to TxAbf furnish hypotheses to explain how the different mutations enhance the T/H ratio (Fig. and related discussion).