Partial purification and thermal characterization of pectinmethylesterase from red grapefruit finisher pulp

Four forms of pectinmethylesterase have been partially purified from red grapefruit finisher pulp by chromatography on Heparin-Sepharose CL6B. Three forms bound to the heparin-sepharose and could be eluted with a sodium chloride gradient. One form (RGPME3) exhibited high thermal stability retaining 66.7% relative activity after 2 min incubation in an 80 degrees C water bath, and 45.2% of its relative activity after 60 sec incubation in a 95 degrees C water bath. RGPME3 had a Km of 0.106 mg. mL-1 citrus pectin and a pH optimum between 6 and 7. The most abundant form (RGPME2) had a Km of 0.079 mg. mL-1 citrus pectin. Denaturing electrophoresis and gel filtration chromatography suggested molecular weights between 20 and 40 kDa for the various forms.