Light-dark regulation of starch metabolism in chloroplasts. II. Effect of chloroplastic metabolite levels on the formation of ADP-glucose by chloroplast extracts
The rate of ADP-glucose formation from (/sup 14/C)glucose 6-phosphate and ATP by the soluble fraction of lysed chloroplasts is studied as a function of the levels of metabolites (3-phosphoglycerate, orthophosphate, hexose monophosphate, and ATP) as determined in whole chloroplasts of Spinacia oleracea in light and dark. A change in 3-phosphoglycerate concentration (from 4 to 1.4 millimolar, as in whole chloroplasts during light-dark transition) decreases the rate of ADP-glucose formation 6- to 7-fold. An increase in hexose monophosphate concentration from 2 to 6 millimolar, which occurs at the same time in whole chloroplasts, stimulates ADP-glucose formation only slightly. At constant levels of orthophosphate (4 millimolar) and 3-phosphoglycerate (4 millimolar), a change in ATP concentration from 0.2 to 1 millimolar causes an immediate 4- to 5-fold increase in the rate of ADP-glucose formation. Another significant stimulation of ADP-glucose formation (about 4- to 6-fold) is obtained after addition of dithiothreitol at high concentrations (50 millimolar). A simultaneous increase in the concentrations of 3-phosphoglycerate, ATP, and dithiothreitol, with orthophosphate and Mg/sup 2 +/ being constant at 4 and 5 millimolar, respectively, causes a 130-fold increase in the rate of ADP-glucose formation (from 0.042 to 5.49 microgram atoms carbon per milligram chlorophyll per hour). The role of these and other factors is discussed with respect to light-dark regulation of starch formation in intact chloroplasts.
- Research Organization:
- Univ. of California, Berkeley
- OSTI ID:
- 5474895
- Journal Information:
- Plant Physiol.; (United States), Journal Name: Plant Physiol.; (United States) Vol. 63; ISSN PLPHA
- Country of Publication:
- United States
- Language:
- English
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59 BASIC BIOLOGICAL SCIENCES
ADP
ATP
BIOCHEMICAL REACTION KINETICS
BIOSYNTHESIS
CARBOHYDRATES
CARBON 14 COMPOUNDS
CELL CONSTITUENTS
CHEMISTRY
CHLOROPLASTS
ISOTOPE APPLICATIONS
KINETICS
LABELLED COMPOUNDS
METABOLISM
METABOLITES
NUCLEOTIDES
ORGANIC COMPOUNDS
OXYGEN COMPOUNDS
PHOSPHATES
PHOSPHORUS COMPOUNDS
PHOTOCHEMISTRY
POLYSACCHARIDES
REACTION KINETICS
REAGENTS
SACCHARIDES
STARCH
SYNTHESIS
TIME DEPENDENCE
TRACER TECHNIQUES