Properties and partial purification of pectin methyl esterase in vegetable-type soybeans

The purpose of this work was to study the effect of sodium chloride, pH, temperature and maturity on soybean pectin methyl esterase activity, to determine enzyme kinetic constants and to describe the inhibition of PME by tannic acid. The enzyme was partially purified. The source of FM£ was a slurry of the soybeans which were raised on the University of Tennessee Plant Science Farm at Knoxville. Beckman Autotitrator was used for enzyme assay. The data reflecting effects of salt concentration, pH, temperature and maturity on PME activity were analyzed by the analysis of variance. The Duncan\u27s Multiple Range Test was employed to determine significant differences among means. In the study of enzyme kinetics, the Lineweaver-Burk double reciprocal form of the Michaelis-Menten was utilized. A FORTRAN computer program was written to determine Km, Vmax, regression coefficient, b,/u\u3e, and the corre-lation coefficient, r, on the IBM 7040 computer. Progressive purification steps for this enzyme were made by acetone-dried powders, salt extraction, ammonium sulfate precipitation, dialysis, and DEAE-cellulose ion-exchange column chromatography. Maximum activity for the PME occurred between 0.25 and 0.40 M concentrations of NaCl, between pH 7.5 and 8.5, and at 50°C. The mean Q10 value was 1.23. The more mature the soybeans were, the lower the total PME activity. The Km value for soybean PME of the first harvest was 0.052 percent pectin and for the third, 0.057 percent pectin. The amount of inhibition of PME by tannic acid was related to inhibitor and substrate concentrations. An increase in PME specific activity of about 140-fold was ob-tained by the purification methods. There were at least two isoenzymes of the soybean FME. This hypothesis is based on the elution behavior of the enzyme on the DEAE-cellulose ion-exchange column