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Articles in PresS, published online ahead of print October 3, 2001
Am J Physiol Cell Physiol, 10.1152/ajpcell.00404.2001
Submitted on August 17, 2001
Accepted on September 25, 2001
1 Biology Department, Carnegie Mellon University, Pittsburgh, PA, USA; Center for Light Microscope, Imaging and Biotechnology, Carnegie Mellon University, Pittsburgh, PA, USA; Pittsburgh NMR Center for Biomedical Research, Carnegie Mellon University, Pittsburgh, PA, USA
* To whom correspondence should be addressed. E-mail: anadir{at}012.net.il.
The function of creatine kinase (CK) and its effect on phosphorus metabolites was studied in livers of transgenic mice expressing the human ubiquitous mitochondrial CK (CK-Mit), the rat brain CK (CK-B) isoenzymes and their combination. 31P NMR spectroscopy and saturation transfer were recorded in livers of anesthetized mice to measure high energy phosphates and hepatic CK activity. CK reaction velocity was related to total enzyme activity irrespective of the isoenzyme expressed, and increased with increasing concentrations of creatine (Cr). The fluxes mediated by both isoenzymes in both directions (PCr or ATP synthesis) were equal. Over a 20 fold increase in CK-Mit activity (28-560 µmol/g wet wt/min), the fraction of phosphorylated Cr increased 1.6 fold. Hepatic free ADP concentrations calculated assuming equilibrium of the CK-catalyzed reaction in vivo decreased from 84±9 to 38±4 nmol/gm wet wt. Calculated free ADP levels in mice expressing high levels of CK-B (920-1635 µmol/g wet wt/min) was 52±6 nmol/gm wet wt. Mice expressing both isoenzymes had calculated free ADP levels of 36±4 nmol/gm wet wt. These findings indicate that CK-Mit catalyzes its reaction equally well in both directions and can lower hepatic apparent free ADP concentrations.
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