Proteomic Analysis of Mature Melanosomes from the Retinal Pigmented Epithelium

The protein content of melanosomes in the retinal pigment epithelium (RPE) was analyzed by mass
spectrometry. More than 100 proteins were found to be common to two out of three variations of
sample preparation. Some proteins normally associated with other organelles were detected. Several
lysosomal enzymes were detected, with the presence of cathepsin D confirmed by immunoelectron
microscopy, thus supporting the previously suggested notion that melanosomes may contribute to
the degradation of ingested photoreceptor outer segment disks.
Keywords: retinal pigment epithelium • melanosome • proteomics