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 ph otosynthesis, is typically a cold-sensitive enzyme, However, a cold-to lerant form of the enzyme has been isolated from the leaves of Flaveri a brownii. Using an E. coli expression system and the PPDK cDNAs from F. brownii (cold-tolerant), F. bidentis (cold-sensitive) and maize (in termediately cold-tolerant), site-directed mutagenesis studies indicat ed that as few as three amino acids residues (of 880 residues) strongl y influence the cold sensitivity of Flaveria PPDK, Gel filtration anal ysis of the PPDK expressed in E. coli showed that subunit association and cold tolerance are closely linked. (C) 1997 Federation of European Biochemical Societies.