Mutagenesis of cysteine 81 prevents dimerization of the APS1 subunit of ADP-glucose pyrophosphorylase and alters diurnal starch turnover in Arabidopsis.

ADP-glucose pyrophosphorylase (AGPase) catalyses the first committed step in the pathway of starch synthesis, the production of ADP-glucose. The enzyme is redox-activated in the light and in response to sucrose accumulation, via reversible breakage of an intermolecular cysteine bridge between the two small (APS1) subunits. In this paper, site directed mutagenesis was used to disrupt the cysteine bridge and investigate how redox modulation of AGPase contributes to the diurnal regulation of starch turnover. 

Hädrich N, Kötting O, Fettke J, Gibon Y, Hendriks JH, Zeeman SC, Steup M, Stitt M, Lunn JE. (2012) .Plant J. 70, 231–242.