PURIFICATION AND CHARACTERIZATION OF FOUR PECTINESTERASES FROM SWEET CHERRY (PRUNUS AVIUM L)

摘要

Four different pectinesterase isoforms, with different isoelectric points, have been detected and purified from sweet cherries (Prunus avium L.): a basic form (PE I, pI >8.66), a neutral form (PE II, pI=7.05), and two acidic forms (PE III, pI=6.36); PE IV, pI=5.24). The molecular weight (MW) of PEI was 35.4 kDa determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and 27.2 kDa determined by filtration through Sephadex G-75 SF. PEs II-IV had the same MW in SDS-PAGE (49.8 kDa) as by filtration through Sephadex G-75 SF (55.9 kDa). PEs I and IV appeared to be the most abundant forms, with K-m values of 1.03 and 74.6 mu g . mL(-1) apple pectin, respectively. The PE isoforms differ in optimum pH and thermal stability, PEs II and IV being the most thermostable. All four isoforms are activated by calcium and sodium cations and inactivated by D-galacturonic acid.