PLANT PHYSIOLOGY , Vol 108, Issue 3 1269-1276, Copyright © 1995 by American Society of Plant Biologists
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BIOCHEMISTRY AND ENZYMOLOGY |
Purification and Properties of a Unique Nucleotide Pyrophosphatase/Phosphodiesterase I That Accumulates in Soybean Leaves in Response to Fruit Removal
M. E. Salvucci and S. J. Crafts-Brandner
United States Department of Agriculture, Agricultural Research Service, Western Cotton Research Laboratory, 4135 East Broadway Road, Phoenix, Arizona 85040-8830
Several unique proteins accumulate in soybean (Glycine max) leaves when the
developing fruits are removed. In the present study, elevated levels 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 native enzyme was likely
octameric. The purified enzyme hydrolyzed nucleotide-sugars, nucleotide di-
and triphosphates, thymidine monophosphate p-nitrophenol, and inorganic
pyrophosphate but not nucleotide monophosphates, sugar mono- and
bisphosphates, or NADH. The subunit and holoenzyme molecular masses and the
preference for substrates distinguish the soybean leaf nucleotide
pyrophosphatase/phosphodiesterase I from other plant nucleotide
pyrophosphatase/phosphodiesterase I enzymes. Also, the N-terminal sequence
of the soybean leaf enzyme exhibited no similarity to the mammalian
nucleotide pyrophosphatase/phosphodiesterase I, soybean vegetative storage
proteins, or other entries in the data bank. Thus, the soybean leaf
nucleotide pyrophosphatase/phosphodiesterase I appears to be a heretofore
undescribed protein that is physically and enzymatically distinct from
nucleotide pyrophosphatase/phosphodiesterase I from other sources, as well
as from other phosphohydrolytic enzymes that accumulate in soybean leaves
in response to fruit removal.
