Phosphorylation/dephosphorylation of the β light chain of clathrin from rat liver coated vesicles

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Abstract
The phosphorylation in vitro, on serine residues by endogenous casein kinase 2, of the clathrin .beta. light chain (33 kDa) of rat liver coated vesicles requires the presence of poly (L-lysine) which acts through binding to the .beta. light chain. The phosphorylation of other protein is also increased in the presence of poly(L-lysine) and casei kinase 2. In contrast, the phosphorylation of the upper band of the 50-kDa protein doublet from rat liver coated vesicles is inhibted. Rat liver coated vesicles display a protein phosphatase activity which preferentially dephosphorylates clathrin .beta. light chain. This activity is different from the protein phosphatase which dephosphorylates the 50-kDa protein. This enzyme seems to be unrelated to the ATP/Mg-dependent protein phosphatase, or the polycation-stimulated protein phosphatases, which dephosphorylate the 50-kDa protein and .beta. light chain very efficiently, but wit a different specificity. After dissociation of coated vesicles the .beta.-light-chain phosphatase activity is recovered in the membrane fraction. This phosphatase activity is inhibted by 50 .mu.M orthovanadate and 5 mM p-nitrophenyl phosphate but not by 10 mM EDTA.
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