Modulation of the activity of purified phosphatidylinositol 4-phosphate kinase by phosphorylated and dephosphorylated B-50 protein |
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Authors: | C J Van Dongen H Zwiers P N De Graan W H Gispen |
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Institution: | 1. Division of Cell Signaling, Fujii Memorial Institute of Medical Sciences, Institute of Advanced Medical Sciences, Tokushima University, 3-18-15 Kuramoto, Tokushima 770-8503, Japan;2. Kuramoto Division, Technical Support Department, Tokushima University, 3-18-15 Kuramoto, Tokushima 770-8503, Japan |
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Abstract: | To investigate the modulation of phosphatidylinositol 4-phosphate kinase activity by the degree of phosphorylation of the B-50 protein, the enzyme was purified from rat brain cytosol by ammonium sulphate precipitation and DEAE-cellulose column chromatography. Purified rat brain B-50 was phosphorylated with protein kinase C and dephosphorylated with alkaline phosphatase. Incubation of the semi-purified phosphatidylinositol 4-phosphate kinase with 1 microgram of the B-50 preparation enriched in the dephospho-form, resulted in a small reduction of phosphatidylinositol 4-phosphate kinase activity (-16%), whereas incubation with the phospho B-50 preparation inhibited the enzyme activity by 40%. The effect of exogenous B-50 was studied in the presence of 10 micrograms albumin to minimize aspecific protein-protein interactions. The present data on the effect of exogenous B-50 protein on phosphatidylinositol 4-phosphate kinase activity, further support our hypothesis that the phosphorylation state of B-50 may be a regulatory factor in phosphoinositide metabolism in rat brain. |
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