Phosphotyrosyl-protein phosphatases. II. Identification and characterization of two heat-stable protein inhibitors.
Two Tyr-protein phosphatase inhibitors, termed inhibitor H (Mr greater than 500,000) and inhibitor L (Mr 38,000), have been detected in bovine brain extracts. The inhibitors were partially purified by chromatography on DEAE-cellulose and Sephacryl S-300. Both inhibitors are proteins, as judged by their inactivation by proteinase K, and they exhibited remarkable stability during incubation at 95 degrees C. Of seven Tyr-protein phosphatase activities that we have isolated from bovine brain, PTP-4 and PTP-5 were most sensitive to the inhibitor proteins. Inhibition of the other five Tyr-protein phosphatases was only observed at very high inhibitor concentrations. The IC50 values for the inhibition of PTP-4 by inhibitor H and inhibitor L were 2- and 10-fold higher than those for the inhibition of PTP-5. Inhibition of PTP-5 by either inhibitor was rapid (maximum effect in less than 1 min) and readily reversed upon removal of the inhibitors by dilution. Inhibitor H and inhibitor L are distinct from the three heat-stable protein inhibitors of Ser/Thr-protein phosphatase 1. The ability of inhibitor H and inhibitor L to preferentially inhibit PTP-4 and PTP-5 provides an important new criterion that can be used to distinguish these enzymes from other Tyr-protein phosphatases. The two inhibitor proteins may be involved in regulating the activity of PTP-4 and PTP-5.
Ingebritsen
T S
TS
Department of Zoology, Iowa State University, Ames 50011.
D000818:Animals; D001921:Brain / Q000201:enzymology*; D002417:Cattle; D006358:Hot Temperature; D007700:Kinetics; D008970:Molecular Weight; D010749:Phosphoprotein Phosphatases / Q000037:antagonists & inhibitors* / Q000378:metabolism; D019000:Phosphotyrosine; D011480:Protease Inhibitors / Q000302:isolation & purification* / Q000378:metabolism; D054645:Protein Phosphatase 1; D014443:Tyrosine / Q000031:analogs & derivatives / Q000378:metabolism
D011480:Protease Inhibitors; D019000:Phosphotyrosine; D014443:Tyrosine; D010749:Phosphoprotein Phosphatases; D054645:Protein Phosphatase 1