Purification of several pectin methyltransferases from cell suspension cultures of flax (Linum usitatissimum L.)

Three pectin methyltransferases (PMT5, PMT7, PMT18; EC 2.1.1.6.x) were solu bilized from the endo-membrane complex of flax cells, with 0.05 % Triton X- 100. After a 3 step-chromatography procedure, PMT7 and PMT5 were purified t o apparent homogeneity. PMT5 and PMT7 differed regarding their optimum pH ( 5 or 7), the methyl acceptor (low or highly methylesterified pectin), their focusing pH range (6-7 or 8-9) and relative molecular mass (40 +/- 5 or 11 0 +/- 10 kDa). SDS-PACE of PMT5 and PMT7 did not reveal bands at 40 or 110 kDa but only a silver stained band of about 18 kDa. Two independent methods (photo labelling and enzymatic activity) showed that this silver-stained b and corresponded to a methyltransferase with affinity For pectins. This pol ypeptide was of the same size as the enzyme designed PMT18 (18 +/- 3 kDa; p l 4-4.5) recovered during size exclusion chromatography of either PMT7 or P MT5, suggesting that PMT18 bears the catalytic site of PMT5 and PMT7. (C) 2 001 Academie des Sciences/Editions scientifiques et medicales Elsevier SAS.