Formation of cyanide from carbon 1 of 1-aminocyclopropane-1-carboxylic acid during its conversion to ethylene

Abstract

It has been shown that 1-aminocyclopropane-1-carboxylic acid (ACC) is the immediate precursor of ethylene, which is derived from C-2 and C-3 of ACC. When [1- 14 C]ACC was administered to etiolated mungbean ( Vigna radiata ) hypocotyls, ≈16% of the ACC was converted to ethylene and about 10% of the radioactivity was converted to [ 14 C]asparagine in 7 hr. In etiolated epicotyls of common vetch ( Vicia sativa ), after 7 hr about 14% of the ACC was converted to ethylene and 16% of the radioactivity was converted to β-cyanoalanine plus γ-glutamyl-β-cyanoalanine. Itis known that in most plants cyanide is metabolized to asparagine via the intermediate β-cyanoalanine, whereas in a fewplants such as V. sativa , β-cyanoalanine is converted to the conjugate γ-glutamyl-β-cyanoalanine. We confirmed that [ 14 C]cyanide was metabolized into [ 14 C]asparagine in mungbean and into [ 14 C]cyanoalanine plus its conjugate in V. sativa . Moreover, after feeding plant tissue with [1- 14 C]ACC, [ 14 C]asparagine isolated from mungbean and β-[ 14 C]cyanoalanine from V. sativa were labeled in the C-4 position, as would be expected if these two compounds were derived from [ 14 C]cyanide. When the conversion of ACC to ethylene in V. sativa tissue was inhibited by high temperature (41°C), the conversion of [1- 14 C]ACC to β-[ 14 C]cyanoalanine and γ-glutamyl-β-[ 14 C]cyanoalanine was similarly inhibited. When [ carboxyl - 14 C]ACC was administered to mungbean and V. sativa , 14 CO 2 was recovered in an amount equivalent to the amount of ethylene produced. These data indicate that in the conversion of ACC to ethylene the carboxyl group yields CO 2 , and C-1 is released as HCN.