IDENTIFICATION OF THE AMINO-ACID-RESIDUES RESPONSIBLE FOR COLD TOLERANCE IN FLAVERIA-BROWNII PYRUVATE,ORTHOPHOSPHATE DIKINASE

Pyruvate, orthophosphate dikinase (PPDK), an enzyme important in C-4 p hotosynthesis, is typically a cold-sensitive enzyme, However, a cold-t olerant form of the enzyme has been isolated from the leaves of Flaver ia brownii. Using an Escherichia coli expression system and the PPDK c DNAs from F. brownii (cold-tolerant), F. bidentis (cold-sensitive) and maize (intermediate cold tolerance), site-directed mutagenesis studie s indicated that as few as three amino acids residues (of 880 residues ) strongly influence the cold sensitivity of Flaveria PPDK. Gel filtra tion analysis of the PPDK expressed in E. coli showed that subunit ass ociation and cold tolerance are closely linked.