Choline kinase in Cuscuta reflexa.
1. Choline kinase is a mitochondrial enzyme in Cuscuta reflexa. It can be solubilized from the particles by treatment with 350mm-sodium chloride, or by freezing and thawing. 2. Choline kinase of C. reflexa was purified by starting from the crude mitochondrial fraction. A 33-52% recovery of the enzyme, on the basis of the activity in the original homogenate, in 1200-2250-fold enrichment, was effected. 3. The purified preparation of choline kinase had a sigmoid saturation curve with respect to choline, with a Hill number of 2.3, and was inhibited by ADP (competitive in nature and allosteric in binding, with a Hill number of 2.7) and by phosphorylcholine (non-competitive and non-allosteric). The kinetic characteristics of the enzyme were consistent with the K type allosteric model of Monod et al. (1965). 4. The enzyme was desensitized, with respect to choline regulation, by prolonged storage in the cold, was activated significantly on warming before assay and was inactivated by high concentrations of sodium chloride. 5. The significance of allostery in choline kinase in relation to the intracellular regulation of phospholipid synthesis is discussed.
D000244:Adenosine Diphosphate; D000494:Allosteric Regulation; D000645:Ammonium Sulfate; D000818:Animals; D001665:Binding Sites; D001667:Binding, Competitive; D002458:Cell Fractionation; D002499:Centrifugation, Density Gradient; D011232:Chemical Precipitation; D002794:Choline; D002848:Chromatography, DEAE-Cellulose; D003080:Cold Temperature; D004355:Drug Stability; D005615:Freezing; D005952:Glucose-6-Phosphatase / Q000032:analysis; D006358:Hot Temperature; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008715:Methionine; D008928:Mitochondria / Q000201:enzymology; D010756:Phosphoric Acids; D010758:Phosphorus; D010770:Phosphotransferases / Q000037:antagonists & inhibitors / Q000302:isolation & purification; D059828:Plant Cells; D010944:Plants / Q000201:enzymology*; D012313:RNA / Q000032:analysis; D012694:Serine; D012965:Sodium Chloride; D013347:Subcellular Fractions / Q000201:enzymology; D013385:Succinate Dehydrogenase / Q000032:analysis
D010756:Phosphoric Acids; D010758:Phosphorus; D012965:Sodium Chloride; D012694:Serine; D000244:Adenosine Diphosphate; D012313:RNA; D008715:Methionine; D013385:Succinate Dehydrogenase; D010770:Phosphotransferases; D005952:Glucose-6-Phosphatase; D002794:Choline; D000645:Ammonium Sulfate