A novel acid phosphatase from Aspergillus niger KU-8 that specifically hydrolyzes C-6 phosphate groups of phosphoryl oligosaccharides.

We had analyzed the detailed structures of the phosphoryl oligosaccharide-1 (PO-1) fraction that was the main component of phosphoryl oligosaccharides (POs) prepared from a potato starch hydrolysate. PO-1 fraction was made up of 3-phosphoryl oligosaccharides and 6-phosphoryl oligosaccharides. Aspergillus niger strain KU-8 produced two types of intracellular acid phosphatase (EC 3.1.3.2, ACPase); ACPase I and II. ACPase II preferentially dephosphorylated 6-phosphoryl oligosaccharides rather than 3-phosphoryl oligosaccharides. The molecular weight of the enzyme was estimated as 66 kDa by SDS-polyacrylamide gel electrophoresis and about 260 kDa by gel filtration, implying the active form to be a tetramer. The optimum pH and temperature of the enzyme were 2.0-2.5 and 60 degrees C, respectively. ACPase II was stable below 50 degrees C for 30 min and pH 2.0-10.0 for 60 min. In spite of the strict specificity toward 6-phosphoryl oligosaccharides in the PO-1 fraction, ACPase II was able to hydrolyze Fru-1,6-di-P, ATP, pyrophosphate, and polyphosphate as well as pNPP and Glc-6-P, a broad substrate specificity.