PLANT PHYSIOLOGY , Vol 106, Issue 3 1151-1156, Copyright © 1994 by American Society of Plant Biologists
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METABOLISM AND ENZYMOLOGY |
Immobilized and Free Apoplastic Pectinmethylesterases in Mung Bean Hypocotyl
M. Bordenave and R. Goldberg
Enzymologie en Milieu Structure, Institut Jacques Monod, 2 Place Jussieu, 75251 Paris Cedex 05, France
The nature and the action pattern of apoplastic pectinmethylesterase (PME)
isoforms were investigated in mung bean [Vigna radiata (L.) Wilzeck]
hypocotyls. Successive extractions of neutral and alkaline PME isoforms
present in hypocotyl native cell walls (referred to as PE1, PE2, PE3, PE4,
with increasingly basic isoelectric points) revealed that solubilization of
PE1, PE2, and PE4 did not induce any significant decrease in the
cell-wall-bound PME activity. The in vitro de-esterification occurring when
isolated cell walls were incubated with pectin resulted, then, from the
activity of PE3. In addition, pH control of PME activity was shown to be
much stronger for enzymes bound to cell walls, in their native state or
reintroduced after solubilization, than for enzymes in solution. Mature
cell walls showed much more activity than young cell walls, and were
relatively enriched in two acidic PME isoforms missing in young cell walls.
One acidic PME was also detected in the extracellular fluid. The acidic and
neutral isoforms that could be easily transferred from their binding sites
to their substrate might be those involved in the demethylation process
developing along the mung bean hypocotyl.
