MULTIPLE FORMS OF PECTIC LYASES AND POLYGALACTURONASE FROM FUSARIUM-OXYSPORUM F-SP RADICIS LYCOPERSICI - REGULATION OF THEIR SYNTHESIS BY GALACTURONIC ACID

The r2 isolate of Fusarium oxysporum f.sp. radicis-lycopersici produce d several pectic enzymes that differ in substrate preference, reaction mechanism, and action pattern. We detected three forms that have lyas e activity, four forms with polygalacturonase activity and one form wi th pectinesterase activity. Lyases had an absolute requirement for cal cium and pIs of 9.20, 9.00, and 8.65. The two more alkaline forms had a weak preference for pectin, whereas the other was mon active on poly galacturonate. Polygalacturonases had pIs of 9.30, 7.35, 6.85, and 6.5 5 and were inhibited by calcium ions. Lyases and polygalacturonases we re induced by galacturonic acid and were subject to catabolite repress ion. Induced synthesis occurred at pHs 5.5 and 8.0 and no increase in lyase activities were promoted by alkalinization of cultures. Pectin l yase had an endo mode of action, whereas pectate lyase and polygalactu ronase behaved more as exoenzymes. These results are discussed in rela tion to the appearance of the different pectic enzymes when the fungus is confronted with a pectic polymer.