MULTIPLE FORMS OF PECTIN METHYLESTERASE FROM CUSCUTA-REFLEXA FILAMENTS

Two multiple forms of pectin methylesterase (EC 3.1.1.11) called A and B forms from the filaments of Cuscuta reflexa have been isolated by DEAE cellulose chromatography. In the present study, both multiple forms have been purified to homogeneity, as estimated by native and SDS polyacrylamide gel electrophoresis, using the techniques of ammonium sulphate fractionation, DEAE cellulose chromatography, gel filtration and ion exchange chromatography on DEAE Sepharose. Both of the multiple forms showed M(r) 60 000 +/- 3000 as determined by Sephadex G-200, as well as SDS-PAGE, indicating monomeric proteins. The isoelectric points of the multiple forms A and B were 9.8 and 8.2, respectively. The K(m)s of PME-A and PME-B for pectin were 0.588 g l(-1) and 0.016 gl(-1) respectively. Mg2+ was an activator of both multiple forms 'K-a' values of PME-A and PME-B for Mg2+ were 0.117 mM and 0.84 mM respectively. Cl- showed a considerable activation of PME-A: ('K-a' value, 4.17 mM), whereas the presence of 5 mM NaCl in the assay mixture is essential for the activity of PME-B.