title: Presence of epsilon-adenosine tetraphosphate in chromaffin granules after transport of epsilon-ATP.
abstract: Adenosine 5'-tetraphosphate (Ap4) is a natural constituent of chromaffin granules with concentration values of 2.2 +/- 0.1 nmol/mg of protein and a ratio 245 +/- 40 times lower with respect to ATP (n = 4). The granular transport of epsilon-ATP resulted in a time- and concentration-dependent production of epsilon-adenosine tetraphosphate (epsilon-Ap4) at the intragranular level. The epsilon-Ap4 formation followed a hyperbolic saturation kinetic at low epsilon-ATP concentrations with K(m) value of 0.4 microM epsilon-ATP intragranular (1.15 pmol/mg of granular protein). Intragranular concentrations of epsilon-ATP higher than 500 pmol/mg of protein (approximately to 175 microM intragranular) resulted in a non-saturable production of epsilon-Ap4.
authors.affiliation: Departamento de Bioquímica, Facultad de Veterinaria, Universidad Complutense, Madrid, Spain.
authors.forename: J
authors.initials: J
authors.lastname: Gualix
authors.forename: M
authors.initials: M
authors.lastname: Abal
authors.forename: J
authors.initials: J
authors.lastname: Pintor
authors.forename: M T
authors.initials: MT
authors.lastname: Miras-Portugal
mesh_terms: D000227:Adenine Nucleotides / Q000302:isolation & purification / Q000378:metabolism*; D000818:Animals; D001692:Biological Transport; D002837:Chromaffin Granules / Q000378:metabolism*; D002851:Chromatography, High Pressure Liquid; D004985:Ethenoadenosine Triphosphate / Q000378:metabolism*; D007700:Kinetics
chemical_list: D000227:Adenine Nucleotides; D004985:Ethenoadenosine Triphosphate; C017991:adenosine 5'-tetraphosphate