Calcium-dependent phosphorylation of a protein in the frog olfactory cilia.
In the cilia of vertebrate olfactory sensory neurons, cytoplasmic Ca(2+) concentration increases in response to odorant stimulation, and this increase has been implicated to have important roles in the regulation of olfactory responses. Since protein phosphorylation is often a regulatory mechanism of biological reactions, we explored the effect of Ca(2+) on phosphorylation reactions in the frog olfactory cilia. First, we found that a 45-kDa phosphoprotein (p45) is predominantly phosphorylated in vitro in the isolated cilia in a Ca(2+)-dependent manner. However, later studies showed that the phosphorylation level of p45 is controlled by a dynamic equilibrium between phosphorylation and dephosphorylation. Although both activities are enhanced at high Ca(2+) concentrations (K(1/2) = approximately 2 microM in both reactions), the enhancement of dephosphorylation is relatively greater than that of phosphorylation. As a result, the steady phosphorylation level of p45 is lower at high than at low Ca(2+) concentration. The phosphorylation/dephosphorylation equilibrium was founed to involve protein kinases sensitive to zinc and heparin, and an unknown phosphatase(s). The present result suggests the presence of a novel Ca(2+)-signaling pathway that involves phosphorylation of p45 in the olfactory cilia.
Katanosaka
Kimiaki
K
Department of Biology, Graduate School of Science, Osaka University, Machikane-yama Toyonaka, Osaka 560-0043, Japan.
Miwa
Naofumi
N
Kawamura
Satoru
S
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D020013:Calcium Signaling / Q000502:physiology; D002923:Cilia / Q000378:metabolism*; D004791:Enzyme Inhibitors / Q000378:metabolism; D009831:Olfactory Mucosa / Q000166:cytology / Q000378:metabolism*; D018034:Olfactory Receptor Neurons / Q000166:cytology / Q000378:metabolism*; D010744:Phosphoric Monoester Hydrolases / Q000037:antagonists & inhibitors / Q000378:metabolism; D010766:Phosphorylation; D011494:Protein Kinases / Q000378:metabolism; D011892:Rana catesbeiana / Q000502:physiology*; D013997:Time Factors
D004791:Enzyme Inhibitors; D011494:Protein Kinases; D010744:Phosphoric Monoester Hydrolases; D002118:Calcium