CHORISMATE MUTASE ISOFORMS FROM SEEDS AND SEEDLINGS OF PAPAVER-SOMNIFERUM

Two isoforms of chorismate mutase (EC 5.4.99.5) were isolated and purified from seeds of Papaver somniferum. A 127-fold purified isoform (CM-1) was inhibited competitively by L-phenylalanine (K(i) = 1.1 mM) and L-tyrosine (K(i) = 0.3 mM) and activated by L-tryptophan (K(a) = 2.4-mu-M), but inhibition by phenylalanine and tyrosine was reversed by tryptophan. The other form (154-fold purified), CM-2, was unaffected by any of the three aromatic amino acids. The K(m) values for chorismate were determined to be 0.14 mM for CM-1 and 0.023 mM for CM-2. M(r) estimated by gel filtration was 84 kDa for CM-1 and 80 kDa for CM-2. M(r) was 55 and 53 kDa, respectively, when determined by PAGE in the presence of SDS. CM-1 is the predominant form in poppy seeds. The ratio of CM-1:CM-2 total activity was determined to be 3:1. In seedlings, CM-2 activity is decreased in age-dependent manner. Five-day-old seedlings contained only CM-1. It was found that CM-1 is located in the chloroplasts of the seedlings.