Inhibition of the catalytic activity of human transaldolase by antibodies and site‐directed mutagenesis

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Abstract
Transaldolase is a key enzyme of the pentose phosphate pathway. While antibody (Ab) 169, directed against the N‐terminal 139 residues of human transaldolase (TAL‐H), had no effect on enzyme activity, Ab 12484 raised against full length and functional recombinant TAL‐H inhibited catalytic activity. This tentatively mapped the catalytic site to the C‐terminal 140–336 amino acid portion of TAL‐H. Dihydroxyacetone transfer reactions catalyzed by transaldolase depend on Schiff base formation by a lysine residue. Replacement of lysine‐142 by glutamine using site‐directed mutagenesis resulted in a complete loss of enzyme activity, suggesting that lysine‐142 is essential for the catalytic activity of TAL‐H.