Separation of thermostable pectinmethylesterase from Marsh grapefruit pulp

A rapid, ion-exchange method that isolates thermostable pectinmethylesteras e (TS-PME) from Marsh grapefruit pulp is presented. TS-PME was selectively extracted with 1 M NaCl and equilibrated at! low pH (3.1 +/- 0.04). After d ilution to a final concentration of 50 mM acetate buffer, pH 5.5, and 0.1, 0.25, or 0.5 M NaCl, the extract was applied to an ion-exchange column with out ammonium sulfate precipitation and dialysis. The percent yield varied f rom an average of 70% (0.1 M NaCl) to 14% (0.5 M NaCl), with a specific act ivity of >400 U/mg protein in the latter sample. TS-PME activity of some co lumn fractions varied compared with crude extracts before column separation . Some fractions lost thermostability after separation if loaded at 0.1 M o r 0.25 M NaCl. In extracts that were loaded at 0.5 M NaCl, the TS-PME: acti vity was significantly higher than that observed in the heated crude extrac ts. Ion-exchange chromatography may have separated an unidentified protecti ve factor in PME fractions.