AMINO-ACID N-MALONYLTRANSFERASES FROM MUNG BEANS - ACTION ON 1-AMINOCYCLOPROPANE-1-CARBOXYLIC ACID AND D-PHENYLALANINE

1-Aminocyclopropane-1-carboxylate (ACC) N-malonyltransferase from etio lated mung bean hypocotyls was examined for its relationship to D-phen ylalanine N-malonyltransferase and other enzymes which transfer malony l groups from malonyl-CoA to D-amino acids. Throughout a 3600-fold pur ification the ratio Of D-phenylalanine N-malonyltransferase activity t o ACC N-malonyltransferase activity was unchanged. Antibodies raised a gainst purified ACC N-malonyltransferase 55-kDa protein were also able to precipitate all D-phenylalanine-directed activity from partially p urified mung bean extracts. The irreversible inhibitors phenylglyoxal and tetranitromethane reduced malonyltransferase activity towards D-ph enylalanine to the same extent as that for ACC. In addition, several o ther D-amino acids, particularly D-tryptophan and D-tyrosine, were abl e to inhibit action towards both ACC and D-phenylalanine. These lines of evidence suggest that a single enzyme is capable of promoting malon ylation of both ACC and D-phenylalanine. K(m) values for D-phenylalani ne and malonyl-CoA were found to be 48 and 43 muM, respectively; these values are 10-fold lower than the corresponding values when ACC was s ubstrate. Coenzyme A was a noncompetitive (mixed type) product inhibit or towards malonyl-CoA at both unsaturated and saturated ACC concentra tions. The enzyme was also inhibited uncompetitively at high concentra tions of malonyl-CoA. We propose that the enzyme follows an Ordered Bi -Bi reaction pathway, with the amino acid substrate being bound initia lly.