PTILOMYCALIN-A, A NOVEL NA-ATPASE OR CA2+-ATPASE INHIBITOR, COMPETITIVELY INTERACTS WITH ATP AT ITS BINDING-SITE(,K+)

Ptilomycalin A inhibited the brain Na+,K+-ATPase and Ca2+-ATPase from skeletal sarcoplasmic reticulum with an IC50 value of 2 mu M and 10 mu M, respectively. Kinetic analysis of the inhibitory effects of ptilom ycalin A suggests that the inhibition of Na+,K+-ATPase is a competitiv e-, an uncompetitive- and an anticompetitive-type with respect to ATP, Na+ and K+, respectively. The inhibition of Ca2+-ATPase by ptilomycal in A is a competitive- or an uncompetitive-type with respect to ATP or Ca2+, respectively. These results suggest that ptilomycalin A interac ts with ATP at the ATP binding site of Na+,K+-ATPase or Ca2+-ATPase. P tilomycalin A has become a useful biochemical tool for clarifying the ATP binding site in both enzymes.