Thiolation of low-Mr phosphotyrosine protein phosphatase by thiol-disulfides.
Thiol-disulfides cause a time- and a concentration-dependent inactivation of the low-M(r) phosphotyrosine protein phosphatase (PTP). We demonstrated that six of eight enzyme cysteines have similar reactivity against 5,5'-dithiobis(nitrobenzoic acid): Their thiolation is accompanied by enzyme inactivation. The inactivation of the enzyme by glutathione disulfide also is accompanied by the thiolation of six cysteine residues. Inorganic phosphate, a competitive enzyme inhibitor, protects the enzyme from inactivation, indicating that the inactivation results from thiolation of the essential active-site cysteine of the enzyme. The inactivation is reversed by dithiothreitol. Although all PTPs have three-dimensional active-site structures very similar to each other and also have identical reaction mechanisms, the thiol group contained in the active site of low-M(r) PTP seems to have lower reactivity than that of other PTPs in the protein thiolation reaction.
Degl'Innocenti
D
D
Dipartimento di Scienze Biochimiche, Università di Firenze, Italy.
Caselli
A
A
Rosati
F
F
Marzocchini
R
R
Manao
G
G
Camici
G
G
Ramponi
G
G
D001665:Binding Sites; D003545:Cysteine / Q000378:metabolism; D004228:Dithionitrobenzoic Acid / Q000378:metabolism / Q000494:pharmacology*; D004789:Enzyme Activation; D019803:Glutathione Disulfide / Q000378:metabolism / Q000494:pharmacology*; D006801:Humans; D007527:Isoenzymes / Q000037:antagonists & inhibitors / Q000378:metabolism; D007700:Kinetics; D008970:Molecular Weight; D010710:Phosphates / Q000494:pharmacology; D017027:Protein Tyrosine Phosphatases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D013439:Sulfhydryl Reagents / Q000378:metabolism / Q000494:pharmacology*
D007527:Isoenzymes; D010710:Phosphates; D013439:Sulfhydryl Reagents; D004228:Dithionitrobenzoic Acid; D017027:Protein Tyrosine Phosphatases; D003545:Cysteine; D019803:Glutathione Disulfide