The control of cellular adenine nucleotides: the discovery and metabolism of an oligomeric derivative of ATP and phosphoglyceric acid in mitochondrial intermembrane space

The comparative content of the mitochondrial phosphoglyceroyl-ATP-containing polymer, purinogen, in rat tissues

Here, we describe an assay for the tissue content of purinogen, a highly phosphorylated labile polymer containing ATP and phosphoglycerate found in the mitochondrial intermembrane space. We report the purinogen content (as adenine nucleotide equivalents) of rat heart and, for the first time, of rat liver, kidney, brain and mixed skeletal muscle. The findings show that purinogen contains very significant proportions of cell adenine nucleotides ranging from 25% of the free pool in brain and skeletal muscle to 135% of it in kidney. The evidence that purinogen may form a controlled intracellular reservoir of inorganic phosphate is briefly discussed.

Differences in nucleotide compartmentation and energy state in isolated and in situ rat heart: assessment by 31P-NMR spectroscopy

Free cytosolic concentrations of ATP, PCr, ADP and 5'-AMP, and the cytosolic [ATP]/[ADP].[Pi] ratio, were determined in isolated and in situ rat hearts using 31P-NMR spectroscopy. Total tissue metabolite concentrations were determined by HPLC analysis of freeze-clamped, perchloric acid-extracted tissue. In in situ myocardium the PCr/ATP ratio was 2.7 +/- 0.2 determined from 31P-NMR data (using either PCr/beta-NTP or PCr/gamma-NTP), and 1.9 +/- 0.1 (P < 0.01) determined from total tissue concentrations. 31P-NMR-determined and total tissue [PCr] were in excellent agreement (49.6 +/- 8.4 and 49.5 +/- 1.0 mumol.g-1 dry wt, respectively), whereas 31P-NMR-determined [ATP] (18.6 +/- 3.2 mumol.g-1 dry wt) was only 71% of the total tissue concentration (26.1 +/- 1.7 mumol.g-1 dry wt, P < 0.01). Isolation and Langendorff perfusion of rat hearts with glucose as substrate reduced total tissue [ATP] and [PCr] and the 31P-NMR-determined PCr/ATP ratio fell to 1.5 +/- 0.1. This value agreed well with the total tissue ratio of 1.4 +/- 0.1, and there was excellent agreement between 31P-NMR-determined and total tissue [PCr] and [ATP] values in the perfused heart. Addition of pyruvate to perfusate increased the 31P-NMR-determined PCr/ATP ratio to 1.7 +/- 0.1 due to elevated [PCr], and there remained excellent agreement between NMR-determined and total tissue [PCr] and [ATP] values. Free cytosolic [ADP] (from the creatine kinase equilibrium) was 5% of total tissue ADP, and free cytosolic [5'-AMP] (from the adenylate kinase equilibrium) ranged from 0.2-0.3% of total tissue 5'-AMP. Bioenergetic state, indexed by [ATP]/[ADP].[Pi], was much lower in isolated perfused hearts (30 mM-1) vs. in situ myocardium (approximately 150 mM-1). In summary, we observe a substantial disproportionality between total tissue PCr/ATP and 31P-NMR-determined PCr/ATP in highly energised in situ myocardium but not in isolated perfused hearts. This appears due to an NMR invisible ATP compartment approximating 29% of total tissue ATP in situ. Additionally, more than 95% of ADP and more than 99% of 5'-AMP exist in bound forms in perfused and in situ myocardium. The physiological significance of these observations is unclear. However, substantial differences between 31P-NMR visible and total tissue [ATP] introduces significant errors in conventional estimation of free cytosolic [ADP], [5'-AMP] and [ATP]/[ADP].[Pi] from in vivo 31P-NMR data.