Catalyzes the conversion of Delta(8)-sterols to their corresponding Delta(7)-isomers. lathosterol = 5alpha-cholest-8-en-3beta-ol zymosterol = 5alpha-cholesta-7,24-dien-3beta-ol Steroid biosynthesis; cholesterol biosynthesis. During interphase, detected on the endoplasmic reticulum and the nuclear envelope. During mitosis, detected on cytoplasmic vesicles. Highly expressed in liver, bowel, adrenal gland, testis, ovary, and uterus and less expressed in brain, cerebellum, skeletal muscle, and heart. Binds to the phenylalkylamine calcium-ion antagonist emopamil, an anti-ischemic drug. Belongs to the EBP family.