Roles of Sucrose-Metabolizing Enzymes in Growth of Seedlings. Purification of Acid Invertase from Growing Hypocotyls of Mung Bean Seedlings

Changes in activities of acid invertase and sucrose synthase during growth of mung bean seedlings were examined and the correlation between the activity of acid invertase and growth was confirmed. Acid invertase was purified from hypocotyls of etiolated seedlings and separated into two fractions (A and B) by chromatography on hydroxylapatite. Acid invertase in fraction B consisted of two polypeptides of 30 kDa and 38 kDa, but that in fraction A was 70 kDa in size. Antibodies raised against the 30-kDa polypeptide immunoprecipitated enzymatic activity but those raised against the 38-kDa polypeptide did not. The concanavalin A-binding site of acid invertase was contained in the 38-kDa polypeptide and not in the 30-kDa polypeptide. However, when acid invertase was bound to and eluted from concanavalin A-Sepharose, the 30-kDa polypeptide was found together with the 38-kDa polypeptide in the eluate. Acid invertase in hypocotyls of mung bean seedlings appears to be present in two forms: a monomer of 70 kDa and a hetero-dimer of 30-kDa and 38-kDa polypeptides. The monomer was not converted to the heterodimer during incubation of a crude extract and was present together with the heterodimer in very young hypocotyls. In older hypocotyls, the heterodimer was present but the monomer was barely detectable. We conclude that the two forms of acid invertase are present within cells, but the relationship between the two forms is unknown at present.