Protein phosphorylation and the two stages of pigment organelle dispersion in permeabilized xanthophores: organelle protein phosphorylation alone supports only the first stage.

We reported previously that, in cultured goldfish xanthophores, dispersion of aggregated carotenoid droplets (CDs) requires the specific phosphorylation of the CD protein p57 by a cAMP-dependent protein kinase and the presence of cytosol. We report here that, in permeabilized cells, the addition of the catalytic subunit of cAMP-dependent protein kinase and ATP phosphorylates p57 and converts the CDs from an immobile to a mobile state (first stage of CD dispersion). However, the CDs are restricted to the vicinity of the original site of the CD aggregate and do not actually disperse (second stage of CD dispersion) unless cytosol is also added. We propose that this process may be related to aspects of secretory processes.