PURIFICATION AND PROPERTIES OF A UNIQUE NUCLEOTIDE PYROPHOSPHATASE PHOSPHODIESTERASE-I THAT ACCUMULATES IN SOYBEAN LEAVES IN RESPONSE TO FRUIT REMOVAL

Several unique proteins accumulate in soybean (Glycine max) leaves whe n the developing fruits are removed. In the present study, elevated le vels of nucleotide pyrophosphatase and phosphodiesterase I activities were present in leaves of defruited soybean plants. The soluble enzyme catalyzing these reactions was purified nearly 1000-fold, producing a preparation that contained a single 72-kD polypeptide. The molecular mass of the holoenzyme was approximately 560 kD, indicating that the n ative enzyme was likely octameric. The purified enzyme hydrolyzed nucl eotide-sugars, nucleotide di- and triphosphates, thymidine monophospha te p-nitrophenol, and inorganic pyrophosphate but not nucleotide monop hosphates, sugar mono- and bisphosphates, or NADH. The subunit and hol oenzyme molecular masses and the preference for substrates distinguish the soybean leaf nucleotide pyrophosphatase/phosphodiesterase I from other plant nucleotide pyrophosphatase/phosphodiesterase I enzymes. Al so, the N-terminal sequence of the soybean leaf enzyme exhibited no si milarity to the mammalian nucleotide pyrophosphatase/phosphodiesterase I, soybean vegetative storage proteins, or other entries in the data bank. Thus, the soybean leaf nucleotide pyrophosphatase/phosphodiester ase I appears to be a heretofore undescribed protein that is physicall y and enzymatically distinct from nucleotide pyrophosphatase/phosphodi esterase I from other sources, as well as from other phosphohydrolytic enzymes that accumulate in soybean leaves in response to fruit remova l.