Catalyzes the transport of triglyceride, cholesteryl ester, and phospholipid between phospholipid surfaces (PubMed:15897609, PubMed:16478722). Required for the assembly and secretion of plasma lipoproteins that contain apolipoprotein B (By similarity). May be involved in regulating cholesteryl ester biosynthesis in cells that produce lipoproteins (By similarity). a 1,2-diacyl-sn-glycero-3-phosphocholine(in) = a 1,2-diacyl-sn-glycero-3-phosphocholine(out) a 1,2-diacyl-sn-glycero-3-phosphoethanolamine(in) = a 1,2-diacyl-sn-glycero-3-phosphoethanolamine(out) a cholesterol ester(in) = a cholesterol ester(out) a triacyl-sn-glycerol(in) = a triacyl-sn-glycerol(out) Heterodimer; heterodimerizes with the protein disulfide isomerase (P4HB/PDI) (By similarity). Interacts with APOB (By similarity). Interacts with PRAP1 (By similarity). Colocalizes with P4HB/PDI in the endoplasmic reticulum.