Substrate selectivity in Aspergillus niger KU-8 acid phosphatase II using phosphoryl oligosaccharides

The intracellular acid phosphatase II (ACPase II) produced by Aspergillus niger KU-8 preferentially dephosphorylates C-6 phosphate groups rather than C-3 phosphate groups of phosphoryl oligosaccharides. In this study, the kinetic parameters of ACPase II were measured. 3(2)-phosphoryl maltotriose and 6(2)-phosphoryl maltotriose, which differ only in the binding position of the phosphate group, were prepared and used as the substrates. The Km for both substrates were similar. However, the k(cat) value for the 6(2)-phosphoryl maltotriose was about three-fold of that for the 3(2)-phosphoryl maltotriose.