The phosphate-pyrophosphate exchange and hydrolytic reactions of the membrane-bound pyrophosphatase of Rhodospirillum rubrum: effects of pH and divalent cations

Journal of Bioenergetics and Biomembranes
H Celis, I Romero

Abstract

The relation that exist between the Pi-PPi exchange reaction and pyrophosphate hydrolysis by the membrane-bound pyrophosphatase of chromatophores of Rhodospirillum rubrum was studied. The two reactions have a markedly different requirement for pH. The optimal pH for hydrolysis was 6.5 Mg2+ or Pi for the enzyme; Mn2+ and Co2+ support the Pi-PPi exchange reaction partially (50%), but the reaction is slower than with Mg2+; other divalent cations like Zn2+ or Ca2+ do not support the exchange reaction. In the hydrolytic reaction, Zn2+, at low concentration, substitutes for Mg2+ as substrate, and Co2+ also substitutes in limited amount (50%). Other cations (Ca2+, Cu2+, Fe2+, etc.) do not act as substrates in complex with PPi. The Zn2+ at high concentrations inhibited the hydrolytic reaction, probably due to uncomplexed free Zn2+. In the presence of high concentration of substrate for the hydrolysis (Mg-PPi) the divalent cations are inhibitory in the following order: Zn2+ greater than Mn2+ greater than Ca2+ greater than or equal to Co2+ greater than Fe2+ greater than Cu2+ greater than Mg2+. The data in this work suggest that H+ and divalent cations in their free form induced changes in the kinetic properties of the enzyme.

References

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Citations

Dec 1, 1992·Journal of Bioenergetics and Biomembranes·I Romero, H Celis
Sep 18, 2004·Journal of Bacteriology·Rodolfo García-ContrerasI Romero
Oct 26, 2005·Archaea : an International Microbiological Journal·Sung-Jong Jeon, Kazuhiko Ishikawa
Oct 18, 2016·International Journal of Biological Macromolecules·Qiong XiaoAnfeng Xiao
Jan 22, 2002·Medical Anthropology·M L Honkasalo

Related Concepts

Cations, Divalent
Hydrogen-Ion Concentration
Hydrolysis
Orthophosphate
Pyrophosphatase
Diphosphates
Rhodospirillum rubrum

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