The rate-determining step in cAMP-mediated exocytosis in the rat parotid and submandibular glands appears to involve analogous 26-kDa integral membrane phosphoproteins.
The possible direct involvement of protein phosphorylation in the regulation of exocytosis during beta-adrenergic receptor stimulation in rat parotid and submandibular salivary glands was investigated in vitro using dispersed cells. The dispersed cells were labeled with [32P]orthophosphate for 40 min prior to experimental manipulation. Subcellular fractions were isolated, the proteins were separated using sodium dodecylsulfate/polyacrylamide gel electrophoresis (NaDodSO4/PAGE), and the phosphoproteins were detected by autoradiography. Changes in the extent of phosphorylation for each phosphoprotein were determined indirectly by densitometric analyses. The analogous parotid and submandibular 26-kDa membrane phosphoproteins had a rapid phosphate turnover rate (t 1/2 = 5-6 min) whereas the analogous 21-kDa membrane phosphoproteins had a much slower phosphate turnover rate (t 1/2 greater than 20 min). The results of Triton X-114 extraction indicated that the 26- and 21-kDa phosphoproteins were integral membrane proteins. The rate of phosphate turnover for the analogous 26-kDa phosphoproteins is compatible with a regulatory role in exocytosis, whereas the slower phosphate turnover rate for the analogous 21-kDa phosphoproteins suggests that these proteins may play a more subordinate role in secretion or they may coordinate secretion with other cellular metabolic events.
Quissell
D O
DO
Deisher
L M
LM
Barzen
K A
KA
D000818:Animals; D000242:Cyclic AMP / Q000502:physiology*; D005089:Exocytosis; D007700:Kinetics; D008297:Male; D008565:Membrane Proteins / Q000502:physiology*; D008970:Molecular Weight; D010306:Parotid Gland / Q000378:metabolism; D010750:Phosphoproteins / Q000502:physiology*; D011494:Protein Kinases / Q000378:metabolism; D051381:Rats; D011919:Rats, Inbred Strains; D011943:Receptors, Adrenergic, beta / Q000502:physiology; D012469:Salivary Glands / Q000378:metabolism*; D013363:Submandibular Gland / Q000378:metabolism
D008565:Membrane Proteins; D010750:Phosphoproteins; D011943:Receptors, Adrenergic, beta; D000242:Cyclic AMP; D011494:Protein Kinases