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The pulsed-field-gradient (PFG) [sup.31]P NMR diffusion spectra were measured under varied sample conditions to characterize the low-affinity binding of adenosine 5'-triphosphate (ATP) on human serum albumin (HSA) or bovine serum albumin (BSA). The NMR diffusion constants of ATP, ATP-HSA, or ATP-BSA were illustrated as function of ATP concentrations. The binding curves of ATP-HSA and ATP-BSA were identical but strikingly different from the ATP curve. Using a 'Scatchard plot', the apparent binding constant (K) and number of ATP binding sites (n) on serum albumin were evaluated as K = 75.25 [(mol/L).sup.-1] and n = 10, respectively. At a pH < 5.0 and a pH > 9.0 or a temperature > 45 °C, the diffusion data of ATP-HSA were found to increase remarkably, suggesting that the dissociation of ATP from HSA was largely enhanced, probably because of pH- or heat-induced protein structural change, degradation, or aggregation. In addition, our data indicated that ADP was strongly competitive with ATP for the low-affinity binding to HSA, but heptanone and [Cl.sup.-] were essentially noncompetitive. These results are important for further elucidating the interaction of ATP with serum albumin and its possible effect on related bioprocesses. The method can be well applied to study the binding of other nucleotides/nucleosides on proteins. Key words: NMR, [sup.31]P, ATP, serum albumin, affinity, diffusion. Operant des diverses conditions de l'echantillon, on a mesure les spectres de diffusion de RMN du [sup.31]P par la methode du gradient de champ pulse (GCP) dans le but de caracteriser la faible affinite de fixation du 5'-triphosphate d'adenosine (TPA) sur de l'albumine serique humaine (ASH) ou de l'albumine serique bovine (ASB). Les constantes de diffusion de RMN du TPA et des agregats TPA-ASH et TPA-ASB sont illustrees en fonction des concentrations du TPA. Les courbes de fixation des agregats TPA-ASH et TPA-ASB sont identiques, mais ils different beaucoup de la courbe du TPA. Faisant appel a la << courbe de Scatchard >>, on a determine que la constante apparente de fixation (K) et le nombre des sites de fixation (n) du TPA sur l'albumine serique sont respectivement de K = 75,25 [(mol/L).sup.-1] et n = 10. A un pH < 5,0 et a un pH > 9,0 ou une temperature > 45 °C, on a observe que les donnees de diffusion pour de l'agregat TPA-ASH augmentent d'une facon remarquable, ce qui suggere que la dissociation du TPA de l'ASH est fortement augmentee, probablement en raison de degradations, d'agregations ou changements structuraux dans la proteine induits par le pH ou la chaleur. De plus, nos donnees suggerent que le diphosphate d'adenosine (DPA) offre une grande competition au TPA pour la fixation de faible affinite avec l'ASH, mais que l'heptanone et l'ion [Cl.sup.-] ne sont pas en competition. Ces resultats sont importants pour une elucidation ulterieure de l'interaction du TPA avec l'albumine serique et des ses effets potentiels sur les bioprocessus apparentes. La methode peut facilement etre appliquee a l'etude de la fixation d'autres nucleotides/nucleosides sur des proteines. Mots-cles: RMN, [sup.31]P, TPA, albumine serique, affinite, diffusion. [Traduit par la Redaction], Introduction Human serum albumin (HSA) is a most abundant protein in blood plasma. It serves as a storage and transport protein for a variety of substances, such as drugs, hormones, [...]

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