STUDIES ON PHYSIOLOGICAL FUNCTION OF ZINC ION-DEPENDENT PHOSPHOTYROSINE PROTEIN PHOSPHATASE

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(1) We have purified two forms, exhibiting molecular weight of approximately 10000 and 62000, of ZnィイD12+ィエD1 -dependent acid phosphatase (ZnィイD12+ィエD1-Apase) from bovine liver. The low-molecular weight (LMW) Zn2+ -APase catalyzed the hydrolysis of myo-inositol-1-phsphate in the presence of 3 mM MgィイD12+ィエD1 at physiological pH, but the high-molecular weight (HMW) enzyme die not. The LMW- ZnィイD12+ィエD1 -Apase of bovine liver was recognized by polyclonal antibodies developed against the ZnィイD12+ィエD1-Apase of bovine brain, but the HMW-AnィイD12+ィエD1APase was not.(2) myo-Inositol monophosphatase from bovine brain exhibited significant hydrolytic activity only on phosphotyrosine among physiological substrates tested in the peresence on ZnィイD12+ィエD1 ions in an acidic environment. The result indicates that myo-inositol monophosphatase exhibits ZnィイD12+ィエD1 -dependent tyrosine phosphatase activity in an acidic environment.(3) The activity and protein level of myo-inositol monophosphatase were in … More vestigated in samples from normal human and Alzhimer's disease (ASD) postmortem brains. In Ad brains myo-inositol monophosphatase activity and its protein level were significantly higher than in control brains. The activity of myo-inositol monophosphatase per enzyme molecule was similar in control and AD brains. These results suggest that myo-inositol monophosphatase is upregulated in AD, probably reflecting compensatory mechanisms concerned with phospholipid metabolism.(4) The distribution of LMW phosphotyrosine protein phosphatase (PTP) in subcellular fractions of rat brain tissue was investigated. The enzyme was abundant in the particulate fraction of nerve endings. LMW-PTP-1 and II were separated from the nerve ending -rich fraction by chromatofocusing. Nerve endings PTP-1 and II were different in molecular weight, isoelectric point and susceptibility to activator and inhibitors. The properties of nerve endings LMW-PTP-1 and II were similar to those of cytosolic LMW-PTP-1 and II. The abundance of LMW-PTP in nerve endings as well as in the cytosol suggests that this enzyme plays an important role in synaptic function. Less