Transport and phosphorylation of choline in higher plant cells. Phosphorus-31 nuclear magnetic resonance studies
When sycamore cells were suspended in basal medium containing choline, the latter was taken up by the cells very rapidly. A facilitated diffusion system appertained at low concentrations of choline and exhibited Michaelis-Menten kinetics. At higher choline concentrations simple diffusion appeared to be the principal mode of uptake. Addition of choline to the perfusate of compressed sycamore cells monitored by /sup 31/P NMR spectroscopy resulted in a dramatic accumulation of P-choline in the cytoplasmic compartment containing choline kinase and not in the vacuole. The total accumulation of P-choline over a 10-h period exhibited Michaelis-Menten kinetics. During this period, in the absence of Pi in the perfusion medium there was a marked depletion of glucose-6-P, and the cytoplasmic Pi resonance disappeared almost completely. When a threshold of cytoplasmic Pi was attained, the phosphorylation of choline was sustained by the continuous release of Pi from the vacuole although at a much lower rate. However, when 100 microM inorganic phosphate was present in the perfusion medium, externally added Pi was preferentially used to sustain P-choline synthesis. It is clear, therefore, that cytosolic choline kinase associated with a carrier-mediated transport system for choline uptake appeared as effective systems for continuously trapping cytoplasmic Pi including vacuolar Pi entering the cytoplasm.
- Research Organization:
- Laboratoire de Physiologie Cellulaire Vegetale, Grenoble (France)
- OSTI ID:
- 5991037
- Journal Information:
- J. Biol. Chem.; (United States), Vol. 264:9
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
CHOLINE
MEMBRANE TRANSPORT
PHOSPHORYLATION
CYTOPLASM
NMR SPECTRA
NUCLEAR MAGNETIC RESONANCE
PHOSPHATES
PHOSPHORUS 31
PHOSPHOTRANSFERASES
PLANT CELLS
SYCAMORES
ALCOHOLS
AMINES
AMMONIUM COMPOUNDS
CELL CONSTITUENTS
CHEMICAL REACTIONS
DRUGS
ENZYMES
HYDROXY COMPOUNDS
ISOTOPES
LIGHT NUCLEI
LIPOTROPIC FACTORS
MAGNETIC RESONANCE
MAGNOLIOPHYTA
MAGNOLIOPSIDA
NUCLEI
ODD-EVEN NUCLEI
ORGANIC COMPOUNDS
OXYGEN COMPOUNDS
PHOSPHORUS COMPOUNDS
PHOSPHORUS ISOTOPES
PHOSPHORUS-GROUP TRANSFERASES
PLANTS
QUATERNARY COMPOUNDS
RESONANCE
SPECTRA
STABLE ISOTOPES
TRANSFERASES
TREES
550201* - Biochemistry- Tracer Techniques