The formation of secondary lysosomes was induced in keratinocytes of guinea pig skin . Lysoso mes labeled by an electron mi croscopi c tracer (Thorotrast) were observed to fuse wi t h and spill their contents in to melanosome co mpl exes and membrane bound sin gle mela nosomes within keratinocytes. Si nce fusions occur only between like or functiona lly related organelles it is conclud ed t hat melanosome complexes and single mela noso mes within keratin ocytes represe nt seconda ry lysosomes .

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... This is supported by the observation t hat these structures conta in acid hydrolases and that melanosome degrad ation takes place in t he labeled melanosome complexes. Fusions were also observed between labeled a nd non-labeled mela nosome complexes and sin gle melanosomes, respective ly, which suggests t hat, in a given population of melanoso me complexes, not all are compl exed during pigment t ransfer but that some are formed de novo within keratinocytes as the product of fu s ion phenomena.