title: Phosphorus-31 nuclear magnetic resonance of aspartate aminotransferase from chicken heart cytosol.
abstract: 31P-nuclear magnetic resonance and absorption spectra of cytosolic chicken aspartate aminotransferase (L-aspartate:2-oxoglutarate aminotransferase, EC 2.6.1.1) have been recorded in the pH range from 5 to 8.5. The 31P chemical shift was found to be pH-dependent with a pK of 6.85; the chemical shift change was 0.35 ppm. The pK value found by spectrophotometric titration of the enzyme proved to be about 6.0. The monoanion-dianion transition of the 5'-phosphate group of a model Schiff base of pyridoxal phosphate with 2-aminobutanol in methanol is accompanied by a change in the 31P chemical shift of 5.2 ppm. It is inferred that the phosphate group of the protein-bound coenzyme is in a dianionic form throughout the investigated pH range; the pH-dependence of the 31P chemical shift may be due to a conformational change at the active site. In the presence of 100 mM succinate, 6 mM aminooxyacetate or 25 mM cycloserine, the 31P chemical shift is insensitive to pH variations.
mesh_terms: D000625:Aminooxyacetic Acid / Q000494:pharmacology; D000818:Animals; D001219:Aspartate Aminotransferases / Q000037:antagonists & inhibitors; D001665:Binding Sites; D002645:Chickens; D003523:Cycloserine / Q000494:pharmacology; D003600:Cytosol / Q000201:enzymology; D006863:Hydrogen-Ion Concentration; D009682:Magnetic Resonance Spectroscopy; D009206:Myocardium / Q000201:enzymology*; D010710:Phosphates; D011487:Protein Conformation; D013386:Succinates / Q000494:pharmacology; D019802:Succinic Acid
chemical_list: D010710:Phosphates; D013386:Succinates; D000625:Aminooxyacetic Acid; D003523:Cycloserine; D019802:Succinic Acid; D001219:Aspartate Aminotransferases