Kinetic characterization of recombinant human cytosolic phosphoenolpyruvate carboxykinase with and without a His10-tag

• Published in: Biochimica et biophysica acta Vol. 1770; no. 11; pp. 1576 - 1584
• Main Authors: Case, Christopher L., Mukhopadhyay, Biswarup
• Format: Journal Article
• Language: English
• Published: Netherlands 01.11.2007
• Subjects: Animals; Cations, Divalent; Cytosol - enzymology; Guinea Pigs; Histidine - metabolism; Humans; Kinetics; Manganese - metabolism; Phosphoenolpyruvate Carboxykinase (GTP) - genetics; Phosphoenolpyruvate Carboxykinase (GTP) - isolation & purification; Phosphoenolpyruvate Carboxykinase (GTP) - metabolism; Rats; Recombinant Proteins - genetics; Recombinant Proteins - isolation & purification; Recombinant Proteins - metabolism; Substrate Specificity - genetics
• ISSN: 0304-4165; 0006-3002
• DOI: 10.1016/j.bbagen.2007.07.012

We report the first kinetic characterization of human liver cytosolic GTP-dependent phosphoenolpyruvate carboxykinase (GTP-PEPCK), which plays a major role in the development of type 2 diabetes in human. In this work two recombinant forms of the enzyme were studied. One form had a His10-tag and the other was His-tag-free, and with one exception, both exhibited similar kinetic properties. When Mn2+ was used as the sole divalent cation, the His10-tagged enzyme, but not the His-tag-free enzyme, was increasingly inhibited at Mn2+ concentrations greater than 0.7 mM. This inhibition did not pose any problem in kinetic analysis, for within the relevant Mn2+ concentration range the His-tagged human PEPCK behaved almost identically to the tag-free enzyme. This property will bring simplicity and speed to purifying and studying multiple structural variants of this important enzyme. Apparent Km values of tag-free enzyme for phosphoenolpyruvate, GDP and bicarbonate were 450, 79 and 20,600 microM, respectively, while those for oxaloacetate and GTP were 4 and 23 microM, respectively, emphasizing the enzyme's gluconeogenic character. Bicarbonate (>100 mM) inhibited OAA-forming activity, which was a new observation with a GTP-PEPCK. The apparent Km for Mn2+ in the PEP-forming direction was 30-fold lower than that for the OAA-forming direction. Mn2+ and bicarbonate or CO2 might regulate the enzyme in vivo.