Naoko Kawakami

Tyrosine phosphorylation and translocation of phospholipase C-γ 2 in polymorphonuclear leukocytes treated with pervanadate

We examined in detail the tyrosine phosphorylation of proteins, especially inositol phospholipid-specific phospholipase C (PLC) gamma 2, during activation of respiratory burst of guinea pig polymorphonuclear leukocytes (PMNs) by pervanadate. The pervanadate, generated from a combination of H2O2 and orthovanadate, induced concomitantly tyrosine phosphorylation of 145, 120, 104, 76, 68, 60, 53, 42, 37, 28, and 25 kDa proteins and superoxide anion (O2-) production of PMNs. The pretreatment of PMNs with genistein caused an inhibition of tyrosine phosphorylation of these proteins, and also markedly depressed O2- production. Among the above proteins, a 145 kDa protein was found to be identical with the protein recognized by the anti-PLC gamma 2 antibody on Western blots. PLC gamma 2 was detected in the cytosol fraction but not in the membrane fraction of resting PMNs, whereas it was detected in both cytosol and membrane fractions of pervanadate treated PMNs. PLC activity of pervanadate treated PMNs was higher than that of resting cells. In addition, the enzyme activity of the cytosol fraction from the former cells was significantly lower than that from the latter cells, whereas the enzyme activity of membrane fraction from the former cells was significantly higher than that from the latter cells. These findings suggest that the tyrosine residue(s) of PLC gamma 2 is phosphorylated and the enzyme is translocated from the cytosol to membrane fractions in PMNs by pervanadate treatment.

myo-Inositol Monophosphatase in the Brain Has Zinc Ion-Dependent Tyrosine Phosphatase Activity

1. myo-Inositol monophosphatase (E.C. 3.1.3.25) hydrolyzes inositol monophosphate to form free myo-inositol, the precursor for the inositol phospholipid second-messenger signaling systems. The biochemical properties of the enzyme were examined in detail. 2. The enzyme exhibited significant hydrolytic activity only on phosphotyrosine among physiological substrates tested in the presence of Zn2+ ions in an acidic environment. 3. The enzyme was recognized and immunoprecipitated with polyclonal antibodies developed against the Zn2+-dependent tyrosine phosphatase of bovine brain. 4. These results indicate that myo-inositol monophosphatase exhibits Zn2+-dependent tyrosine phosphatase activity in an acidic environment and has immunological identity with a Zn2+-dependent tyrosine phosphatase.