SOYBEAN ROOT-NODULE ACID-PHOSPHATASE

Acid phosphatases are ubiquitous enzymes that exhibit activity against a variety of substrates in vitro, although little is known about thei r intracellular function. In this study we report the isolation, chara cterization, and partial sequence of the major acid phosphatase from s oybean (Glycine max L.) root nodules. The phosphatase was purified pre dominantly as a heterodimer with subunits of 28 and 31 kD; homodimers of both subunits were also observed and exhibited phosphatase activity . In addition to the general phosphatase substrate, p-nitrophenyl phos phate, the heterodimeric form of the enzyme readily hydrolyzed 5'-nucl eotides, flavin mononucleotide, and O-phospho-1-Tyr. Low or negligible activity was observed with ATP or polyphosphate. Purified nodule acid phosphatase was stimulated by magnesium, inhibited by calcium and EDT A, and competitively inhibited by cGMP and cAMP with apparent K-i valu es of 7 and 12 mu M, respectively. Partial N-terminal and internal seq uencing of the nodule acid phosphatase revealed homology to the soybea n vegetative storage proteins. There was a 17-fold increase in enzyme activity and a noticeable increase in protein levels detected by immun oblotting methods during nodule development. Both of these parameters were low in young nodules and reached a peak in mature, functional nod ules, suggesting that this enzyme is important for efficient nodule me tabolism.