On the mechanism of activation of protein kinase FA (an activating factor of ATP.Mg-dependent protein phosphatase) in brain myelin |
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Authors: | Shiaw-Der Yang Jau-Song Yu Chih-Wei Hua |
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Affiliation: | (1) Institute of Life Science, National Tsing Hua University, Hsinchu;(2) Institute of Molecular Cell Biology, Chang Gung Medical College, Tao-Yuan, Taiwan, ROC |
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Abstract: | Protein kinase FA (an activating factor of ATP·Mg-dependent protein phosphatase) has been characterized to exist in two forms in the purified brain myelin. One form of kinase FA is spontaneously active and trypsin-labile, whereas the other form of kinase FA is inactive and trypsin-resistant, suggesting a different membrane topography with active FA exposed on the outer face of the myelin membrane and inactivu FQ buried within the myelin membrane. When myelin was solubilized in 1% Triton X-100, all kinase FA became active and trypsin-labile. Phospholipid reconstitution studies further indicated that when kinase FA was reconstituted in acidic phospholipids, such as phosphatidylinositol and phosphatidylserine, the enzyme activity was inhibited in a dose-dependent manner, suggesting that kinase FA interacts with acidic phospholipids which inhibit its activity. Furthermore, when myelin was incubated with exogenous phospholipase C, the inactive/trypsin-resistant FA could be converted to the active/trypsin-labile FA in a time- and dose-dependent manner. Taken together, it is concluded that membrane phospholipids play an important role in modulating the activity of kinase FA in the brain myelin. It is suggested that phospholipase C may mediate the activation-sequestration of inactive/trypsin-resistant kinase FA in the brain myelin through the phospholipase C-katalyzed degradation of acidic membrane phospholipids. The activation-sequestration of protein Kinase FA may represent one mode of control modulating the activity of kinase FA in the central nervous system myelin. |
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Keywords: | Protein kinase protein phosphatase brain myelin membranes phospholipids |
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