Possible involvement of adenylylation in the modification of a 26 kDa protein in rat parotid acinar cells.

1. Adenylylation, a posttranslational modification of proteins, was investigated in saponin-permeabilized acinar cells of the rat parotid gland. 2. When cells were incubated with [2,8-3H]ATP, several proteins, including a 26 kDa protein in the particulate fraction, were labeled. 3. Upon incubation of cells with [alpha-32P]ATP in the presence of cAMP and 3-isobutyl-1-methylxanthine, 32P-labeling of the 26 kDa protein was observed. 4. After treatment with snake venom phosphodiesterase, [32P]AMP was released from the 26 kDa protein. Such release was not observed when cells were labeled with [gamma-32P]ATP. 5. The 32P-labeling pattern of proteins with [alpha-32P]ATP was clearly different from that with [adenylate-32P]NAD+. 6. The results suggest that the 26 kDa protein is one of the adenylylation substrates in rat parotid acinar cells.