Comparison of the hydrolysis of Zn-PPi2- and the MgPPi2- as substrates and the effect of free cations upon membrane-bound pyrophosphatase of Rhodospirillum rubrum.
The hydrolytic activity of chromatophore membrane-bound pyrophosphatase with Zn-PPi2- as substrate was studied and compared with Mg-PPi2- hydrolysis. The pH profile of Zn-PPi2- hydrolysis is a bell shaped curve with an optimum at 5.25. This behavior is different from the sigmoidal profile obtained for Mg-PPi2- hydrolysis, which has a plateau from pH 6.5 to 9.0. Zn-PPi2- hydrolytic activity is inhibited by 1-butanol and methylene-diphosphate but not by NaF. The enzyme has no activity when free Zn2+ concentration is lower than 7.5 pM (at 0.9-1.2 mM Zn-PPi2-) and therefore free Zn2+ is an essential activator of Zn-PPi2- hydrolytic activity. Free Mg2+, on the contrary, acts as an inhibitor of Zn-PPi2- hydrolysis. The dependence of the reaction rate on the Zn-PPi2- concentration is sigmoidal.
Romero
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I
Departamento de Bioenergética, Universidad Nacional Autónoma de México.
Celis
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H
D001426:Bacterial Proteins / Q000378:metabolism*; D002412:Cations; D011756:Diphosphates / Q000378:metabolism*; D004791:Enzyme Inhibitors; D006863:Hydrogen-Ion Concentration; D006868:Hydrolysis; D007700:Kinetics; D008274:Magnesium; D008565:Membrane Proteins / Q000378:metabolism*; D011755:Pyrophosphatases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D012247:Rhodospirillum rubrum / Q000201:enzymology*; D013379:Substrate Specificity; D015032:Zinc
D001426:Bacterial Proteins; D002412:Cations; D011756:Diphosphates; D004791:Enzyme Inhibitors; D008565:Membrane Proteins; D011755:Pyrophosphatases; D008274:Magnesium; D015032:Zinc