Rice endosperm-specific plastidial alpha-glucan phosphorylase is important for synthesis of short-chain malto-oligosaccharides.
Arch Biochem Biophys
; 495(1): 82-92, 2010 Mar 01.
Article
en En
| MEDLINE
| ID: mdl-20045390
ABSTRACT
Previous genetic studies have indicated that the type L alpha-glucan phosphorylase (Pho1) has an essential role during the initiation process of starch biosynthesis during rice seed development. To gain insight into its role in starch metabolism, we characterized the enzymatic properties of the Pho1 recombinant form. Pho1 has significantly higher catalytic efficiency toward both linear and branched alpha-glucans in the synthesis direction than in the degradation direction with equilibrium constants for the various substrates ranging from 13 to 45. Pho1 activity is strongly inhibited by its own reaction product (Pi) in the synthesis reaction (K(i)=0.69 mM) when amylopectin is the primer substrate, but this inhibition is less pronounced (K(i)=14.2 mM) when short alpha-glucan chains are used as primers. Interestingly, even in the presence of Pi alone, Pho1 not only degrades maltohexaose but also extends them to synthesize longer MOSs. Production of a broad spectrum of MOSs (G4-G19) was stimulated by both Pi and Glc1P in an additive fashion. Thus, even under physiological conditions of high Pi/Glc1P, Pho1 extends the chain length of short MOSs which can then be used as subsequent primer by starch synthase activities. As ADP-glucose strongly inhibits Pho1 activity, Pho1 likely operates only during the initial stage and not during maturation phase of starch synthesis.
Texto completo:
1
Colección:
01-internacional
Base de datos:
MEDLINE
Asunto principal:
Oligosacáridos
/
Proteínas de Plantas
/
Oryza
/
Endospermo
/
Fosforilasas
Idioma:
En
Revista:
Arch Biochem Biophys
Año:
2010
Tipo del documento:
Article
País de afiliación:
Estados Unidos