Structure/activity Relationship of Thapsigargin Inhibition on the Purified Golgi/secretory Pathway Ca2+/Mn2+ Transport ATPase (SPCA1a) — Structure/activity relationship of thapsigargin inhibition on the purified Golgi/secretory pathway Ca2+/Mn2+-transport ATPase (SPCA1a) — Inhibition of SPCA1a by thapsigargin