Multiple forms of phosphatase from human brain: Isolation and partial characterization of affi-gel blue binding phosphatases

Implication of protein phosphatases in Alzheimer disease led us to a system ic 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 phosphatase s. Affi-gel blue-binding phosphatases were further separated into four diff erent phosphatases, designated P1, P2, P3, and P4 by calmodulin-Sepharose 4 B and poly-(L-lysine) agarose chromatographies. These four phosphatases exh ibited activities towards nonprotein phosphoester and two of them, PI and P 4, could dephosphorylate phosphoproteins. The activities of the four phosph atases differed in pH optimum, divalent metal ion requirements, sensitiviti es to various inhibitors and substrate affinities. The apparent molecular m asses 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 bra in and rabbit skeletal muscle. P4 was labeled with anti-PP2A antibody and m ay represent a new subtype of PP2A. P1 and P4 were also effective in dephos phorylating Alzheimer disease abnormally hyperphosphorylated tau (AD P-tau) . The resulting dephosphorylated AD P-tau had its activity restored in prom oting assembly of microtubules in vitro. These results suggest that P1 and P4 might be involved in the regulation of phosphorylation of tau in human b rain, especially in neurodegenerative conditions like Alzheimer's disease w hich are characterized by the abnormal hyperphosphorylation of this protein .