PRESENCE OF EPSILON-ADENOSINE TETRAPHOSPHATE IN CHROMAFFIN GRANULES AFTER TRANSPORT OF EPSILON-ATP

Adenosine 5'-tetraphosphate (Ap(4)) is a natural constituent of chroma ffin granules with concentration values of 2.2 +/- 0.1 nmol/mg of prot ein and a ratio 245 +/- 40 times lower with respect to ATP (n = 4). Th e granular transport of epsilon-ATP resulted in a time- and concentrat ion-dependent production of epsilon-adenosine tetraphosphate (epsilon- Ap(4)) at the intragranular level. The epsilon-Ap(4) formation followe d a hyperbolic saturation kinetic at low epsilon-ATP concentrations wi th K-m value of 0.4 mu M epsilon-ATP intragranular (1.15 pmol/mg of gr anular protein). Intragranular concentrations of epsilon-ATP higher th an 500 pmol/mg of protein (approximate to 175 mu M intragranular) resu lted in a non-saturable production of epsilon-Ap(4).