Deciphering the kinetic mechanisms controlling selected plant ADP-glucose pyrophosphorylases.
Arch Biochem Biophys
; 535(2): 215-26, 2013 Jul 15.
Article
em En
| MEDLINE
| ID: mdl-23603314
ABSTRACT
ADP-Glc pyrophosphorylase (AGPase), a rate-limiting enzyme in starch biosynthesis, is controlled by thermostability and allosteric regulation. Previous studies suggested that redox affects turnover number and heat stability of AGPases. Here, we investigated how allostery and redox state affect kinetic mechanisms of the reduced, heat labile and the oxidized, heat stable potato tuber enzymes; the heat labile maize endosperm enzyme and a chimeric maize/potato heat stable enzyme that lacks the cysteine responsible for redox changes. With 3-PGA, all AGPases followed a Theorell-Chance Bi Bi mechanism with ATP binding first and ADP-Glc releasing last. 3-PGA increases the binding affinity for both substrates with little effect on velocity for the maize and MP isoforms. By contrast, 3-PGA increases the velocity and the affinity for G-1-P for the potato enzymes. Redox state does not affect kcat of the two potato isoforms. Without 3-PGA the oxidized potato enzyme exhibits a rapid equilibrium random Bi Bi mechanism with a dead end ternary complex. This fundamental change from rapid, ordered binding with little buildup of intermediates to a mechanism featuring relatively slow, random binding is unique to the oxidized potato tuber enzyme. Finally, ADP-Glc the physiologically relevant product of this enzyme has complex, isoform-specific effects on catalysis.
Texto completo:
1
Coleções:
01-internacional
Base de dados:
MEDLINE
Assunto principal:
Proteínas de Plantas
/
Glucose-1-Fosfato Adenililtransferase
Idioma:
En
Revista:
Arch Biochem Biophys
Ano de publicação:
2013
Tipo de documento:
Article
País de afiliação:
Estados Unidos