Enzymatic properties of separated isozymes of the Na,K-ATPase: substrate affinities, kinetic cooperativity, and ion transport stoichiometry

摘要: There are two isozymes of the Na,K-ATPase, which can be purified separately from rat renal medulla and brainstem axolemma. Here basic kinetic properties Na,K-ATPases have been compared in conditions permitting enzyme turnover. The half-maximally activated at different concentrations ATP, axolemma Na,K-ATPase having higher affinity. They by Na+ K+ very similar but show differences cooperativity toward Na+. affinities both for ATP affected a qualitatively way variations concentration K+. Both transport 22Na+ 42K+ ratio close to 3:2 artificial lipid vesicles. differ most strikingly inhibition ATPase activity ouabain. has high affinity ouabain with positive cooperativity, while lower negative cooperativity. It is likely that due effects, reflecting rates conformation transitions during functional result contrasting cooperativities difference sensitivity amplified.