Abstract

In potassium bromide pellets, 1 Eq of Mg⁺⁺ shifted all four infrared phosphate bands of adenosine triphosphate to higher frequencies, whereas in aqueous solution (Irtran cuvette) only the P=O peak was displaced (from 1225 to 1240 cm^-1). These effects can be interpreted by hydratioin of the P=O moiety and chelation of the metal by the β- and γ-phosphate groups. At both pH 3 and 7, 4 Eq of norepinephrine shifted the P=O and P⁺—O^- peaks in KBr pellets to lower frequencies. The displacement of the P⁺—O^- band can be attributed to association of the amine cation with the ATP anion. Since this process would be expected to cause P=O absorption at a higher frequency, it appears probable that the hydroxyl groups of the ethanolamine moieties form hydrogen bonds with the P=O groups. This formulation is attractive on stereochemical grounds. Mixtures of ATP, norepinephrine, and Mg⁺⁺ yielded spectra similar to those from the nucleotide and the metal alone. Thus, in solution, Mg⁺⁺ has a greater affinity than norepinephrine for ATP. Nevertheless, the spectra of the soluble contents of bovine adrenal medullary granules as well as intact granules resembled those of mixtures of catecholamines and ATP devoid of metals. These observations provide the first direct evidence for catecholamine. ATP complexes in granules. However, they leave undetermined the possibility that alkaline earth metals may play a role in the storage of catecholamines.