VARIABLE HEAT-STABILITY FOR MULTIPLE FORMS OF PECTIN METHYLESTERASE FROM CITRUS TISSUE-CULTURE CELLS

Six forms of pectin methylesterase from Citrus sinensis var. Valencia juice sec derived tissue culture cells have been partially purified by anion-exchange and affinity (heparin and concanavalin A) chromatography. Data on thermal stability and thermal denaturation are provided. One of these forms (PME 3b) retained 29% activity after being incubated at 95 degrees C for 30 s. Two other forms also retained activity at 80-90 degrees C. The most active form, accounting for 93.6% of total activity at 30 degrees C, was completely inactivated after 2 min of incubation at 80 degrees C. The most heat stable form, PME 3b, has a K-m of 0.0309 mg mL(-1) and a V-max of 1.4596 mu equiv min(-1). PME 3b has a pH optimum of 7.0 and is glycosylated. Denaturing electrophoresis and native gel filtration chromatography suggest molecular weights between 34 000 and 47 000 for the partially purified PMEs. The molecular weight of PME 3b estimated by LDS-PAGE was 37 500 and that estimated by gel filtration chromatography was 40 600.