Purification and properties of aldose 1-epimerase from Aspergillus niger

Aspergillus niger ATCC 6274 was selected as an aldose 1-epimerase (EC 5.1.3.3) producer from 45 stock cultures of A. niger. The aldose 1-epimerase was purified 115-fold to apparent homogeneity from cell extracts with a yield of 2.6%. The molecular weight was calculated to be 260,000 and that of the subunit to be 130,000. The enzyme preparation was active at pH 5-7. The Km value was 50 mM and the V value was 1200 units/mg toward alpha-D-glucose. This enzyme catalyzed mutarotation of the following substrates; alpha-D-glucose, beta-D-fructose, beta-L-arabinose and beta-D-galactose. The time required for glucose determination with a glucose oxidase reagent was significantly shortened by the addition of aldose 1-epimerase.