Phosphoenolpyruvate carboxylase from Rumex dentatus, a C-3-plant

PEPC activity was measured in the root tips and in mature sections of Rumex dentatus, a C-3 plant. The level of PEPC is low in 10 mm root tips from seedlings but relatively high in mature root sections taken at 20 to 35 mm from the tip. When root tips are excised there is a marked increase in PEPC over a 12-h period. In mature root sections, on the other hand, the PEPC activity declines over the same 12-h period. The increase in the root tips is sensitive to cordycipin, G-methylpurine, cycloheximide and actinomycin D, which indicates that both RNA and protein synthesis are involved in the formation of PEPC in the root tip sections. The enzyme was inhibited by aspartate and tricarboxylic acid cycle intermediates, while activation by any of the compounds was not observed. The enzyme is located in the cytoplasm of the root cells. PEPC was markedly inhibited by adenine nucleotides: AMP, ADP and ATE ADP was the most effective, at least in the presence of an excess of MgCl2. The inhibition by nucleotides suggests regulation by energy charge. PEPC was inhibited by tetranitromethane, butanedione, diethylpyrocarbonate and N-ethylmalemide, and reveals the presence of lysyl, arginyl, histidyl and thiol groups as essential residues in the enzyme. PEPC responded in a consistent manner to applied GA(3) depending upon the growth period of seedlings. PEPC is a threonine-sensitive enzyme, although it is only little sensitive to histidine.