cAMP-dependent protein kinase phosphorylates gap junction protein in lens cortex but not in lens nucleus.

MP70 (a 70 kDa membrane protein) is a component of the gap junctions of the young fibre cells in the lens outer cortex. In the older fibres deeper in the mammalian lens (lens nucleus), MP70 is processed to MP38 by cleavage and removal of the carboxy terminal half. It is shown here that cortical MP70, and its derivative MP64, can be phosphorylated with cAMP-dependent protein kinase. In contrast, MP38 from the lens nucleus is not phosphorylated by the enzyme. Proteolytic processing and this lens region specific phosphorylation are relevant for the future development of functional assays for lens gap junctions.