A mutation in the large subunit of tobacco Rubisco reduces the decline in activity during catalysis

摘要

The gene encoding the Rubisco large subunit of tobacco has been mutated specifically at codon 335 using plastid transformation, converting it to encode valine instead of leucine (Whitney et al. 1999). Leu-335 is located on loop 6 of the large subunit, adjacent to the catalytically important Lys-334 residue. The Leu-335 residue also makes van der Waals contacts with the P2 phosphate of the substrate. As a result of this substitution, the mutant enzyme's maximal carboxylation rate and specificity forCO_2 were reduced to less than 25 percent of the wild-type values. The Michaelis constants for CO_2, O_2 and D-ribulose-1,5-bisphosphate (RuBP) were also reduced. Further studies have now been carried out to determine the effect of the mutation on otheractivities in the active site.