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Phosphotyrosine phosphatase activity in human placenta.
The Japanese Journal of Experimental Medicine
|February 1, 1985
Summary
Researchers purified a human placenta enzyme that dephosphorylates phosphotyrosine. This specific phosphotyrosine phosphatase exhibits distinct properties from other phosphatases, suggesting a unique biological role.
Area of Science:
- Biochemistry
- Enzymology
- Human Physiology
Background:
- Phosphotyrosine phosphatases are crucial enzymes involved in cellular signaling.
- Understanding human placenta phosphatases is important for developmental biology and disease research.
Purpose of the Study:
- To isolate and characterize a phosphotyrosine phosphatase from human placenta.
- To investigate the substrate specificity and kinetic properties of the purified enzyme.
- To differentiate this enzyme from known acid and alkaline phosphatases.
Main Methods:
- Enrichment of phosphotyrosine phosphatase from human placenta homogenates.
- Utilized ammonium sulfate fractionation, P-cellulose, and Phenyl Sepharose chromatography.
- Enzyme activity assays using phosphotyrosine, p-nitrophenyl phosphate, and phosphoenol-pyruvate.
Main Results:
- Achieved a 9-fold enrichment of phosphotyrosine phosphatase activity.
- The enzyme hydrolyzed phosphotyrosine, p-nitrophenyl phosphate, and phosphoenol-pyruvate.
- Optimal activity at pH 7.0; enzyme exhibited instability and altered Km during purification.
- Copper ions (Cu2+) completely inhibited activity, while zinc ions (Zn2+) showed slight inhibition.
- Differential inhibitor effects on phosphotyrosine vs. p-nitrophenyl phosphate hydrolysis were observed.
Conclusions:
- The purified human placenta enzyme possesses phosphotyrosine phosphatase activity.
- Its substrate profile and inhibitor sensitivity differ from classical acid and alkaline phosphatases.
- These findings suggest the presence of a distinct phosphotyrosine phosphatase in human placenta.