Some size and charge properties of tomato pectin methylesterase

Abstract

Commercial tomato pectin methylesterase has been separated into 4–6 protein fractions by gel filtration on Sephadex G-75 and G-200. The molecular weights of these fractions ranged from 6800 to more than 235 000. The enzyme was localized in only one fraction, in which the distribution of enzyme activity essentially paralleled that of ultraviolet absorbance. On analytical column gel filtration and on thin-layer gel filtration on Sephadex G-75, the molecular weight of the enzyme was found to be 24 000 and 27 000, respectively. A possible interaction of the enzyme with the dextran gel was excluded by thin-layer gel filtration on the polyacrylamide Bio-Gel P-60, a molecular weight of 28 000 being obtained. Ultracentrifugal analysis of the enzyme isolated by preparative gel filtration followed by (NH 4) 2SO 4 precipitation gave an s 0 20, w value of 3.3 S. The molecular weight determined by sedimentation equilibrium was 26 300. The frictional ratio was calculated to be 1.17. Electrophoretic heterogeneity of the commercial enzyme preparation and of some of the fractions isolated by preparative gel filtration was demonstrated by paper electrophoresis. The isoelectric point of pectin methylesterase was found to be 8.4 at 20° by thin-layer isoelectric focusing.