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. Defects in Ebp are a cause of 'Tattered' (Td) which is an X-linked, semidominant mouse mutation associated with prenatal male lethality. Heterozygous females are small and at 4 to 5 days of age develop patches of hyperkeratotic skin where no hair grows, resulting in a striping of the coat in adults. Craniofacial anomalies and twisted toes have also been observed in some affected females. Binds to the phenylalkylamine calcium-ion antagonist emopamil, an anti-ischemic drug. Belongs to the EBP family.