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 CL‐6B. 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°C water bath, and 45.2% of its relative activity after 60 set incubation in a 95°C water bath. RGPME3 had a K m of 0.106 mg * mL −1 citrus pectin and a pH optimum between 6 and 7. The most abundant form (RGPMEZ) had a K m 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.