BIOSYNTHESIS OF LYSINE IN PLANTS - THE PUTATIVE ROLE OF MESO-DIAMINOPIMELATE DEHYDROGENASE

Extracts from Chlamydomonas, corn, soybean and tobacco were tested for enzymes of the lysine biosynthetic pathway. Dihydrodipicolinic acid ( DHD) synthase, DHD reductase, diaminopimelate (DAP) epimerase and DAP decarboxylase were present in all. However, in contrast to the report of Wenko et al., meso-DAP dehydrogenase could not be detected in extra cts prepared from soybean. Moreover, it was not found in Chlamydomonas , corn and tobacco as well. In order to set an upper limit to the amou nt of meso-DAP dehydrogenase that might be present, reconstruction exp eriments were performed with soybean and corn extracts in which the co nversion of dihydrodipicolinate to lysine was made dependent on the ad dition of limited amounts of the meso-DAP dehydrogenase purified from Bacillus sphaericus. The presence of DAP epimerase and the absence of meso-DAP dehydrogenase indicates that the meso-DAP dehydrogenase abbre viated pathway for lysine synthesis is not operative in plants.