PURIFICATION AND CHARACTERIZATION OF A PECTIN LYASE FROM PYTHIUM SPLENDENS INFECTED CUCUMBER FRUITS

A pectin lyase (PL, EC 4.2.2.10) was produced by Pythium splendens Bra un in infected cucumber fruits. The enzyme was purified to near homoge neity by ammonium sulfate fractionation, CM - Sepharose column chromat ography, and preparative isoelectric focusing. The enzyme had a molecu lar mass of 23 kDa as determined by SDS-PAGE. The pi of the PL was 8.0 , which was also the optimum pH for the enzyme activity. The enzyme wa s stable at 4-50 degrees C, but beyond 50 degrees C, its activity decr eased rapidly. The pectin lyase degraded high methyl-esterified pectin by trans-elimination in an endo-manner, and was stimulated by some di valent cations including Ca2+, Mg2+, and Sr2+. Addition of Zn2+ inhibi ted the enzyme activity by 36%. The purified PL caused rapid maceratio n of potato and cucumber discs. This is the first report of a FL produ ced by Pythium splendens, a plant pathogenic fungus which causes seedl ing damping-off and fruit rot in cucumber.