Open AccessThe Reactions between Active and Inactive Forms of Wheat Ribulosebisphosphate Carboxylase and Effectors
Author(s) -
GUTTERIDGE Steven,
PARRY Martin A. J.,
SCHMIDT C. N. Godfrey
Publication year - 1982
Publication title -
european journal of biochemistry
Language(s) - English
Resource type - Journals
eISSN - 1432-1033
pISSN - 0014-2956
DOI - 10.1111/j.1432-1033.1982.tb06822.x
Subject(s) - effector , pyruvate carboxylase , chemistry , carboxylation , rubisco , enzyme , biochemistry , enzyme activator , ribulose 1,5 bisphosphate , biophysics , stereochemistry , biology , catalysis
The processes of activation and deactivation of ribulose‐1,5‐bisphosphate carboxylase purified from wheat have been investigated. Two forms of the enzyme are indistinguishable in terms of ribulose‐1,5‐bisphosphate carboxylation and oxidation but exhibit different rates of activation. One form is slowly activated in saturating CO 2 and Mg 2+ at moderate temperatures ( t 0.5 ∼ 120 min at 25°C), the other form rapidly activated ( t 0.5 ∼ 8 s). In the presence of the effectors 6‐phosphogluconate or NADPH, significantly lower concentrations of the activating co‐factors can achieve full activation of both enzyme species. However, with another effector, fructose 1,6‐bisphosphate, for the slowly activating species the mode of action is the same as with 6‐phosphogluconate or NADPH, whereas the activation of the rapidly activating species is significantly inhibited. The substrate, ribulose 1,5‐bisphosphate, also inhibits this rapid activation process. A mechanism is proposed for the reactions involving activation that accounts for the differential rates of activation and the response to effectors.