KINETICS OF NA-ATPASE INHIBITION BY A RAT-BRAIN ENDOGENOUS FACTOR (II-E)(, K+)

Previous work from this laboratory led to the isolation by gel filtrat ion and anionic exchange HPLC of a rat brain fraction named II-E, whic h highly inhibits synaptosomal membrane Na+, K+-ATPase activity. In th is study we evaluated the kinetics of such inhibition and found that i nhibitory potency was independent of Na+ (1.56-200 mM), K+ (1.25-40 mM ), or ATP (1-8 mM) concentration. Hanes-Woolf plots indicated that II- E decreases Vmax but does not alter K-M value, and suggested uncompeti tive inhibition for Na+, K+ or ATP. However, II-E became a stimulator at 0.5 mM ATP concentration. It is postulated that this brain factor m ay modulate ionic transport at synapses, thus participating in central neurotransmission.