NITRIC-OXIDE CAUSES INACTIVATION OF THE LOW-MOLECULAR-WEIGHT PHOSPHOTYROSINE PROTEIN PHOSPHATASE

The low M(r) phosphotyrosine protein phosphatase (PTPase) and Yersinia enterocolitica PTPase are inactivated by nitric oxide-generating comp ounds. Inorganic phosphate, a competitive inhibitor, protects the enzy mes from inactivation, suggesting that the action of NO is directed to the active sites. Low M(r) PTPase from bovine liver lost two out of e ight thiol groups present in the molecule during the inactivation with sodium nitro prusside and with other NO-producing compounds. The mass spectrometric analyses of tryptic fragments of the enzyme, performed after chemical modification of the NO-unreacted thiol groups, demonstr ated that NO caused the oxidation of Cys-12 and Cys-17 to form an S-S bond. A similar reaction was described previously for the reaction of NO with N-methyl-D-aspartate receptor. The NO-inactivated low M(r) PTP ase was reactivated by treating the inactive enzyme with thiol-contain ing reagents. Since all members of the PTPase family have the same rea ction mechanism and possess a conserved active site motif that contain s an essential cysteine residue, the findings on low M(r) and Yersinia PTPases are potentially interesting for all PTPases, an enzyme class that is involved in a number of important biological processes.