PARTIAL-PURIFICATION AND PROPERTIES OF A 36-KDA 1-AMINOCYCLOPROPANE-1-CARBOXYLATE N-MALONYLTRANSFERASE FROM MUNG BEAN

A 36-kDa 1-aminocyclopropane-1-carboxylate (ACC) N-malonyltransferase, which converts the ethylene precursor ACC into the conjugated derivat ive malonyl-ACC (MACC), has been isolated from etiolated mung bean (Vi gna radiata) hypocotyls, and partially purified in a four-step procedu re. The enzyme is stimulated about 7-fold by 100 mM K+ salts or 0.5 mM Co2+ salts, and is inhibited competitively by D-phenylalanine (K-i = 1.3 mM) and non competitively by CoASH (0.3 mM). Beside malonyl-CoA, i t is capable to use succinyl-CoA as an acyl donor. The 36-kDa enzyme d escribed here exhibits a lower optimum temperature (40 degrees C) and a 7- or 3-fold lower apparent K-m for ACC (68 mu M) and malonyl-CoA (7 4 mu M). respectively, when compared with its 55 kDa isoform already i solated from the same plant material. This data support the idea that several isoforms of ACC N-malonyltransferase exist in plants. These is oforms may play a differential role in regulating the availability of ACC, and consequently the rate of ethylene production, as well as deto xifying cells from D-amino acids.