A fluorescent marker for autophagic vacuoles; autofluorescent substance incorporated into multilamellar bodies by both an ion trapping mechanism and interaction with membrane lipids; exhibits Stokes shift and increased relative fluorescence in hydrophobic environments; selectively accumulates in PaTu 8902 subcellular fractions containing the lysosomal enzymes acid phosphatase and cathepsin D, but not those containing the rough and smooth endoplasmic reticulum markers TRAM and cytochrome P450, respectively