Acid phosphatase of potato tubers (Solanum tuberosum L). Purification, properties, sugar and amino acid composition.

1. Acid phosphatase (AcPase) from potato tubers was purified by tannic acid fractionation, DEAE-cellulose chromatography, filtration on Bio-Gel P-150 and affinity chromatography on Con A-Sepharose. The enzyme was purified 260-fold and was electrophoretically homogeneous; its mol. mass is about 69 000. 2. The carbohydrate component accounts for 16.6% of the total enzyme weight and includes mannose (5.6%), rhamnose (3.4%), glucose (2.5%), galactose (1.5%) and glucosamine (3.6%). In the amino acid composition aspartic acid, glutamic acid, serine and glycine account for 37.7% of total amino acid residues. 3. Optimum pH is at 5.0-5.3. The enzyme activity was reduced by half after 30 min incubation at 60 degrees C, and was fully abolished after 2 h incubation at 70 degrees C. The enzyme is a nonspecific phosphomonoesterase; aromatic phosphomonoesters and inorganic pyrophosphate can serve as substrates. Apparent Km values were 1.25 mM and 40 mM for p-nitrophenylphosphate and inorganic pyrophosphate, respectively. The enzyme is inhibited by MoO42-, Zn2+, Hg2+ and urea. Inhibition caused by urea was reversible at urea concentration below 9 M.