Mechanism of inhibition of protein-tyrosine phosphatases by vanadate and pervanadate.
Vanadate and pervanadate (the complexes of vanadate with hydrogen peroxide) are two commonly used general protein-tyrosine phosphatase (PTP) inhibitors. These compounds also have insulin-mimetic properties, an observation that has generated a great deal of interest and study. Since a careful kinetic study of the two inhibitors has been lacking, we sought to analyze their mechanisms of inhibition. Our results show that vanadate is a competitive inhibitor for the protein-tyrosine phosphatase PTP1B, with a Ki of 0.38+/-0.02 microM. EDTA, which is known to chelate vanadate, causes an immediate and complete reversal of the inhibition due to vanadate when added to an enzyme assay. Pervanadate, by contrast, inhibits by irreversibly oxidizing the catalytic cysteine of PTP1B, as determined by mass spectrometry. Reducing agents such as dithiothreitol that are used in PTP assays to keep the catalytic cysteine reduced and active were found to convert pervanadate rapidly to vanadate. Under certain conditions, slow time-dependent inactivation by vanadate was observed; since catalase blocked this inactivation, it was ascribed to in situ generation of hydrogen peroxide and subsequent formation of pervanadate. Implications for the use of these compounds as inhibitors and rationalization for some of their in vivo effects are considered.
Huyer
G
G
Department of Biochemistry and Molecular Biology, Merck Frosst Centre for Therapeutic Research, Kirkland, Quebec, Canada.
Liu
S
S
Kelly
J
J
Moffat
J
J
Payette
P
P
Kennedy
B
B
Tsaprailis
G
G
Gresser
M J
MJ
Ramachandran
C
C
D000818:Animals; D004492:Edetic Acid / Q000494:pharmacology; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D006861:Hydrogen Peroxide / Q000494:pharmacology; D007700:Kinetics; D013058:Mass Spectrometry; D017027:Protein Tyrosine Phosphatases / Q000037:antagonists & inhibitors*; D014638:Vanadates / Q000494:pharmacology*
D004791:Enzyme Inhibitors; C076715:pervanadate; D014638:Vanadates; D004492:Edetic Acid; D006861:Hydrogen Peroxide; D017027:Protein Tyrosine Phosphatases