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Kanamori, T., Hayakawa, T., Suzuki, M. & Titani, K. (1995) Identification of two 17-kDa rat parotid gland phosphoproteins, subjects for dephosphorylation upon b-adrenergic stimulation, as destrin- and cofilin-like proteins. J. Biol. Chem. 270, 8061-8067.


We previously reported that when 32Pi-loaded rat parotid slices are incubated with the
b-adrenergic agonist isoproterenol, the level of a soluble 32P-labeled 17-kDa protein (pp17) decreases rapidly (Kanamori, T., and Hayakawa, T.(1982) Biochem. Int. 4, 517-523). Here we show that pp17 consists of two distinct phosphoproteins (pp17a and pp17b), identify their unphosphorylated forms (p17a and p17b, respectively), and provide evidence for their b-adrenergic stimulation-induced dephosphorylation. Since p17a and p17b were predominant forms even in nonstimulated cells, peptides were generated from them with Staphylococcus aureus V8 protease or cyanogen bromide; subsequent sequencing of these peptides and homology search allowed identification of p17a and p17b as destrin- and cofilin-like proteins, respectively. Interestingly, they were also dephosphorylated in response to cholinergic stimulation. Because destrin and cofilin are actin-depolymerizing proteins whose activities are possibly regulated by their phosphorylation/dephosphorylation, the two parotid proteins reported here might be involved in cortical F-actin disruption observed in parallel with exocytotic amylase secretion.
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