title: Bovine brain Na+, K+-stimulated ATP phosphohydrolase studied by a rapid-mixing technique. Detection of a transient [32P]phosphoenzyme formed in the presence of potassium ions.
abstract: 1. Conditions for binding of [gamma-32P]ATP to bovine brain Na+,K+-stimulated ATPase were investigated by the indirect technique of measuring the initial rate of 32P-labelling of the active site of the enzyme. 2. At 100 muM [gamma-32P]ATP in the presence of 3 mM MgCl2, approximately the same very high rate of formation of [32P]phosphoenzyme was obtained irrespective of whether [gamma-32P]ATP was added to the enzyme simultaneously with, or 70 ms in advance of the addition of NaCl. A comparatively slow rate of phosphorylation was obtained at 5 muM[gamma-32P]ATP without preincubation. However, on preincubation of the enzyme with 5 muM[gamma-32P]ATP a rate of formation of [32P]phosphoenzyme almost as rapid as at 100 muM[gamma-32P]ATP was observed. 3. A transient [32P]phosphoenzyme was discovered. It appeared in the presence of K+, under conditions which allowed extensive binding of [gamma-32P]-ATP. The amount of [gamma-32P]ATP that could be bound to the enzyme seemed to equal the amount of [32P] phosphorylatable sites. 4. The formation of the transient [32P] phosphoenzyme was inhibited by ADP. The transient [32P] phosphoenzyme was concluded mainly to represent the K+-insensitive and ADP-sensitive E1-32P. 5. When KCl was present in the enzyme solution before the addition of NaCl only a comparatively slow rate of phosphorylation was observed. On preincubation of the enzyme with [gamma-32]ATP an increase in the rate of formation of [32P] phosphoenzyme was obtained, but there was no transient [32P]-phosphoenzyme. The transient [32P]phosphoenzyme was, however, detected when the enzyme solution contained NaCl in addition to KCl and the phosphorylation was started by the addition of [gamma-32P]ATP.
mesh_terms: D000251:Adenosine Triphosphatases / Q000378:metabolism*; D000818:Animals; D002417:Cattle; D002540:Cerebral Cortex / Q000201:enzymology*; D004789:Enzyme Activation / Q000187:drug effects; D007700:Kinetics; D008433:Mathematics; D008722:Methods; D009994:Osmolar Concentration; D010750:Phosphoproteins / Q000378:metabolism*; D010761:Phosphorus Radioisotopes; D011188:Potassium / Q000494:pharmacology*; D012964:Sodium / Q000494:pharmacology*; D013997:Time Factors
chemical_list: D010750:Phosphoproteins; D010761:Phosphorus Radioisotopes; D012964:Sodium; D000251:Adenosine Triphosphatases; D011188:Potassium