Multiple Forms of Phosphatase from Human Brain: Isolation and Partial Characterization of Affi-Gel Blue Binding Phosphatases |
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Authors: | Cheng Li Yao Wang Jian-Zhi Gong Cheng-Xin Pei Jin-Jing Zaidi Tanweer Grundke-Iqbal Inge Iqbal Khalid |
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Institution: | (1) Department of Neurochemistry, New York State Institute for Basic Research in Developmental Disabilities, Staten Island, New York, 10314;(2) Present address: Department of Biochemistry, Faculty of Medicine, National University of Singapore, 10 Kent Ridge Crescent, Singapore, 119260;(3) Department of Pathophysiology, Tongji Medical University, Wuhan, 430030, P.R. China;(4) Department of Geriatric Medicine, Karolinska Institutet B56-K, S-141 86 Huddinge, Sweden;(5) Department of Neurochemistry, New York State Institute for Basic Research in Developmental Disabilities, Staten Island, New York, 10314 |
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Abstract: | Implication of protein phosphatases in Alzheimer disease led us to a systemic investigation of the identification of these enzyme activities in human brain. Human brain phosphatases eluted from DEAE-Sephacel with 0.22 M NaCl were resolved into two main groups by affi-gel blue chromatography, namely affi-gel blue-binding phosphatases and affi-gel blue-nonbinding phosphatases. Affi-gel blue-binding phosphatases were further separated into four different phosphatases, designated P1, P2, P3, and P4 by calmodulin-Sepharose 4B and poly-(L-lysine)-agarose chromatographies. These four phosphatases exhibited activities towards nonprotein phosphoester and two of them, P1 and P4, could dephosphorylate phosphoproteins. The activities of the four phosphatases differed in pH optimum, divalent metal ion requirements, sensitivities to various inhibitors and substrate affinities. The apparent molecular masses as estimated by gel-filtration for P1, P2, P3, and P4 were 97, 45, 42, and 125 kDa, respectively. P1 is markedly similar to PP2B from bovine brain and rabbit skeletal muscle. P4 was labeled with anti-PP2A antibody and may represent a new subtype of PP2A. P1 and P4 were also effective in dephosphorylating Alzheimer disease abnormally hyperphosphorylated tau (AD P-tau). The resulting dephosphorylated AD P-tau had its activity restored in promoting assembly of microtubules in vitro. These results suggest that P1 and P4 might be involved in the regulation of phosphorylation of tau in human brain, especially in neurodegenerative conditions like Alzheimer's disease which are characterized by the abnormal hyperphosphorylation of this protein. |
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Keywords: | Phosphatases human brain calcineurin microtubule assembly microtubule associated protein tau Alzheimer's disease |
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