THE MODE OF INHIBITORY-ACTION OF ALPHA-MANGOSTIN, A NOVEL INHIBITOR, ON THE SARCOPLASMIC-RETICULUM CA2-PUMPING ATPASE FROM RABBIT SKELETAL-MUSCLE()

alpha-Mangostin, the principal ingredient of the fruit hull of Garcini a mangostana, caused a concentration-dependent decrease in the activit ies of both Ca2+-ATPase and Ca2+-transport of the sarcoplasmic reticul um from rabbit skeletal muscle with an IC50 value of 5 mu M. Neither C a2+ release nor other enzyme activities were affected by alpha-mangost in. Kinetic analysis of the inhibitory effects of alpha-mangostin on C a2+-ATPase suggests that the inhibition of the ATPase is a noncompetit ive-type with respect to ATP or Ca2+. alpha-Mangostin may become a use ful pharmacological tool for clarifying the physiological functions of Ca2+-pumping ATPase and sarcoplasmic reticulum.