Evidence that the recently discovered high-energy nucleotide derivative, oligo(phosphoglyceroyl-ATP) forms the end chains of purinogen, a complex polymeric major storage form of adenine nucleotide and phosphate in heart.

Previous work in our laboratory has shown that free adenine nucleotides in heart, liver and kidney exchange rapidly with a major acid-insoluble species which we have characterised as oligo[3-phospho-glyceroyl-gamma- triphospho(5')adenosine(3')], abbreviated to (PG-ATP)n. This has been found in liver and in heart to be complexed to a specific 3'-phosphodiesterase which releases PG-ATP monomers and is located in mitochondrial inter-membrane space. In [14C]adenosine-perfused hearts, (PG-ATP)n has been shown to reach specific radioactivity equilibrium with free ATP within 30 min. Attempts to estimate the quantities of nucleotide in (PG-ATP)n and free nucleotides in response to a variety of stimuli using previously labelled hearts showed by contrast that the free and sequestered nucleotide pools were not at equilibrium. Re-examination of the rapidly labelled acid-insoluble species led to the recognition of radioactive inhomogeneity and of three additional nucleotide components. Perfusion of hearts with phosphate-free medium increased the proportion of 14C incorporated into the sequestered from by 70% and caused the net transfer of 0.9 mumol.g-1 of purine from free adenine nucleotides to the sequestered form. The findings point to the existence of a more complex polymer whose rapidly exchanging end chains we had previously isolated and characterised as (PG-ATP)n; we suggest the name purinogen for this polymer and show that it can contain between 25% and 55% of the tissue nucleotide pool in rat heart.