PURIFICATION AND PROPERTIES OF PECTINESTERASES OF MARSH WHITE GRAPEFRUIT PULP

Thermolabile (TL) and thermostable (TS) pectinesterases (PE) were purified 124- and 309-fold, respectively, from Marsh white grapefruit pulp by ion-exchange and gel filtration chromatography. Thermolabile PE accounted for the majority of PE activity (90%) in crude extracts. Native M(r) values of TL PE and TS PE were estimated to be 36 000 and 51 000, respectively, and both enzymes were composed of a single polypeptide chain. Carbohydrate content was estimated at 2% for TL PE and 14.2% for TS PE. Amino acid content, antigenic properties, and UV spectra served to distinguish the enzymes. The K(m) values (Sunkist pectin substrate) of TL and TS PEs were 0.274 and 1.02 mg/mL, respectively. Turnover numbers were 26 354 and 30 621 mol/(mol.min) for TL and TS PEs, respectively.