Studies on the regulation of 1-aminocyclopropane-1-carboxylate synthase in tomato using monoclonal antibodies

A partially purified preparation of 1-aminocyclopropane-1-carboxylate (ACC) synthase (EC 4.4.1.14) from tomato (Lycopersicon esculentum (Mill.) fruit tissue was used to generate monoclonal antibodies (MAb) specific for the two different MAbs yielded a 50-kDa polypeptide as shown by sodium dodecylsulfate-polyacrylamide gel electrophoresis. An enzyme-linked immunosorbent assay (ELISA) capable of detecting <1 ng of antigen was developed. The ELISA system was used to demonstrate that two of the MAbs recognized different epitopes on the ACC-synthase protein. Wound-induced increases in ACC-synthase activity in tomato fruit tissue were correlated with changes in ELISA-detectable protein. In-vivo labeling of wounded tissue with [35S]methionine followed by extraction and immunopurification in the presence of various protease inhibitors yielded one major radioactive band of 50 kDa molecular mass. Pulse labeling with [35S]methionine at various times after wounding indicated that the wound-induced increase in ACC-synthase activity involved de-novo synthesis of a rapidly turning over 50-kDa polypeptide.