Partial purification and properties of a 36‐kDa 1‐aminocyclopropane‐1‐carboxylate N‐malonyltransferase from mung bean

Abstract

A 36‐kDa 1‐aminocyclopropane‐1‐carboxylate (ACC) N‐malonyltransferase, which converts the ethylene precursor ACC into the conjugated derivative malonyl‐ACC (MACC), has been isolated from etiolated mung bean (Vigna radiata) hypocotyls, and partially purified in a four‐step procedure. 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 (Ki= 1.3 mM) and non competitively by CoASH (0.3 mM). Beside malonyl‐CoA, it is capable to use succinyl‐CoA as an acyl donor. The 36‐kDa enzyme described here exhibits a lower optimum temperature (40°C) and a 7‐ or 3‐fold lower apparent Km for ACC (68 μM) and malonyl‐CoA (74 μM), respectively, when compared with its 55 kDa isoform already isolated from the same plant material. This data support the idea that several isoforms of ACC N‐malonyltransferase exist in plants. These isoforms may play a differential role in regulating the availability of ACC, and consequently the rate of ethylene production, as well as detoxifying cells from D‐amino acids.