IMMUNOPURIFICATION AND CHARACTERIZATION OF A 40-KD 1-AMINOCYCLOPROPANE-1-CARBOXYLIC ACID N-MALONYLTRANSFERASE FROM MUNG BEAN SEEDLING HYPOCOTYLS

1-Aminocyclopropane-1-carboxylic acid (ACC) N-malonyltransferase catal yzes the transfer of the malonyl group from malonyl coenzyme A to ACC to form malonyl ACC. Using partially purified ACC N-malonyltransferase from the hypocotyls of mung bean (Vigna radiata) seedlings, we produc ed two mouse monoclonal antibodies (1H5 and 2G3) to this enzyme. These antibodies bind to sites other than the active site of the enzyme bec ause monoclonal antibody-bound ACC N-malonyltransferase still exhibits full catalytic activity. A monoclonal antibody column was constructed using 1H5 and protein G Sepharose. The ACC N-malonyltransferase purif ied from this monoclonal antibody column has a molecular mass of 40 kD , which is different from that reported previously. The enzyme has a h igher electrophoretic mobility on sodium dodecyl sulfate-polyacrylamid e gel electrophoresis in the absence of the reducing agent dithiothrei tol. The optimum temperature of this 40-kD ACC N-malonyltransferase is 45 degrees C and the apparent K(m)s for ACC and malonyl coenzyme A ar e 66.7 and 40 mu M, respectively.