Ethylene biosynthesis-inducing protein from cellulysin is an endoxylanase

The proteinaceous ethylene biosynthesis-inducing factor (EIF) that was purified from Cellulysin was also shown to contain a xylanase activity. In all nondenaturing protein separation methods employed (Sephacryl S-200 chromatography, and preparative isoelectric focusing and agarose electrophoresis), xylanase activity copurified with the ethylene biosynthesis-inducing activity. Treatment with heat (60°C) or proteases in 8 molar urea inhibited both ethylene-inducing and xylanase activities. Antibodies raised against purified EIF, which contains three polypeptides of 18, 14, and 10 kilodaltons, immunoprecipitated both ethylene biosynthesis-inducing and xylanase activities. The purified EIF contained no detectable cellulase, polygalacturonase, or protease activity. Other hydrolytic activities as estimated by using p-nitrophenyl derivatives of several sugars as substrates also were not detected. Different commercially available hydrolytic enzyme preparations were tested for both ethylene biosynthesis-inducing and xylanase activities. All enzymes tested contained xylanase activity, but only a few induced ethylene biosynthesis. Western blots of proteins separated by SDS-PAGE, using antibodies prepared against the non-denatured purified EIF, revealed two major bands of about 18 and 14 kilodaltons in EIF. These antibodies seem to be specific for these proteins from Trichoderma viride, because there was little cross-reactivity with the other proteins in Cellulysin and other commercial enzyme preparations. Based on these data, we suggest that EIF contains a specific xylanase activity which is involved in inducing ethylene biosynthesis.