PURIFICATION AND PROPERTIES OF ACID-PHOSPHATASE SECRETED FROM LUPIN ROOTS UNDER PHOSPHORUS-DEFICIENCY CONDITIONS

When lupin plants were grown in phosphorus-deficient nutrient solutions, the activity of acid phosphatase secreted from their roots remarkably increased in comparison with that under adequate phosphorus conditions. Based on activity staining of acid phosphatase on IEF gels, many isozymes mere present in roots and leaves, but one of these was mainly secreted into the rhizosphere. This main acid phosphatase secreted from roots was purified from the phosphorus-deficient nutrient solution where lupin was grown, using ion exchange chromatography with DEAE-Sepharose CL-6B, gel filtration with Bio-Gel P-200, and preparative-PAGE. The molecular weight of the purified enzyme was estimated to be 72,000 by SDS-PAGE and approximately 140,000 by gel filtration. Thus, this enzyme was considered to be a homo-dimer. The isoelectric point and the optimum pH of the enzyme were 4.7 and 4.3, respectively.