| Abstract: | Pectinmethylesterases (EC 3.1.1.11
EC]
) have been solubilized fromyoung and mature tissues of mung bean hypocotyls. Whatever theplastic potential of the tissues, most of the pectinmethylesteraseactivity was located in the cell walls. Several active fractionswere obtained after chromatography on CM Sépharose. Equilibriumsedimentation in an analytical ultracentrifuge indicated theMW of the isolated isoforms to be close to 75 000 whereas SDS-PAGEelectrophoresis gave a MW around 32 000, suggesting the possibilityof dimeric structures. Mung bean pectinmethylesterase (PME)showed cross reactivity with soybean antiserum. Experiments carried out with p-nitrophenylacetate and Citruspectin revealed that PME and esterase activities might correspondto different isoforms. It was also noted that the stimulationinduced by cations was stronger when the enzymes were boundto the cell walls. The high ionic sensitivity suggested that,in situ, the ionic environment regulates pectinmethylesteraseactivity principally by modifying the pectin molecules, whichenhances the affinity of the enzymes for their substrate. Thesedata indicate the importance of the calcium content of the cellwalls and might explain the decrease in methylated pectins alongthe mung bean hypocotyl and, in turn, the loss of plasticity. Key words: Cell wall, hypocotyl, pectinmethylesterase, Vigna radiata |
