PRESENCE AND PROPERTIES OF DIAMINOPIMELIC ACID DECARBOXYLASES IN GENUS CRITHIDIA

1. 1. The flagellate Crithidia fasciculata can be grown in a completely defined, lysine containing medium. It has been shown that lysine can be replaced by α,ε{lunate}-diaminopimelic acid (30:70 mixture of the l- and meso-isomers or either of them separately) but not by dl-α-aminoadipic acid. No lysine could be detected in the samples of diaminopimelic acid used, and the growth responses of the organism to equimolar amounts of the diaminopimelic acid and lysine were identical. [3H]-Diaminopimelic acid was incorporated into the hot trichloroacetic acid-insoluble fraction of organisms as lysine, and the amount of this incorporation was markedly reduced if lysine was present in the incubation medium. These results suggest that C. fasciculata contains a diaminopimelic acid decarboxylase and possibly a diaminopimelix acid epimerase. 2. 2. Diaminopimelic acid decarboxylase activity was detected in acetone powders of both C. fasciculata and Crithidia oncopelti by a spectrophotometric method. The enzyme in C. oncopelti was found to be specific for the meso isomer of diaminopimelic acid and to have a pH optimum in phosphate buffer of about 7.5. The amount of activity in C. fasciculata was found to be very small; its presence was confirmed by an assay using [3H]diaminopimelic acid. 3. 3. No diaminopelic acid decarboxylase activity was detected in extracts of the culture forms of Trypanosoma rhodesiense or Trypanosoma cruzi or in homogenates of rat liver. © 1969.