Binding of 2-acetylpyridine-5-[(2-chloroanilino)thiocarbonyl] thiocarbonohydrazone (BW348U87) to human serum albumin.
Dissociation constants and rate constants for the binding of 2-acetylpyridine-5-[(2-chloroanilino)thiocarbonyl]thiocar bonohydrazone (I, BW348U87), an agent that enhances the antiherpetic efficacy of acyclovir, to human serum albumin have been determined. I quenched the fluorescence of human serum albumin, whereas the absorbance of I at 370 nm increased upon binding to the protein. The absorbance change was attributed to preferential binding of anionic I (pKa 7.0). Titration data indicated multiple binding sites for I. The dissociation constant of the high-affinity site was 0.11 microM. The time course for binding of I to 100 nM human serum albumin was biphasic. The early and late phases were described by first-order rate constants that had maximal values of 100 and 11 sec-1, respectively. The rate constant for the dissociation of I from human serum albumin was estimated to be 6 sec-1. Dodecyl sulfate and octanoate displaced I from human serum albumin.I with rate constants of 4.5 and 7.3 sec-1, respectively. Since the fluorescence emission spectrum of human serum albumin and the absorption spectrum of I overlapped significantly (the spectral overlap integral, J, was 2.6 x 10(-14) M-1 cm3), the possibility of Förster dipole-dipole energy transfer was considered. However, a significant fraction of the fluorescence quenching by I resulted from a conformational change in the protein upon binding of I and was not the result of dipole-dipole energy transfer. Nonetheless, the distance between one of the binding regions for I on human serum albumin and a tryptophan residue in the protein was estimated to be 31 A by this method. The high affinity of I for albumin could be related to its low hematological toxicity.
Porter
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Experimental Therapy Division, Wellcome Research Laboratories, Research Triangle Park, NC 27709.
D000212:Acyclovir / Q000378:metabolism; D000998:Antiviral Agents / Q000378:metabolism*; D001665:Binding Sites; D002210:Caprylates / Q000737:chemistry; D006801:Humans; D006835:Hydrazones / Q000737:chemistry / Q000378:metabolism*; D007700:Kinetics; D011487:Protein Conformation / Q000187:drug effects; D011725:Pyridines / Q000737:chemistry / Q000378:metabolism*; D012709:Serum Albumin / Q000378:metabolism*; D012967:Sodium Dodecyl Sulfate / Q000737:chemistry; D013056:Spectrophotometry, Ultraviolet; D013816:Thermodynamics; D014364:Tryptophan
D000998:Antiviral Agents; D002210:Caprylates; D006835:Hydrazones; D011725:Pyridines; D012709:Serum Albumin; C069703:compound 348U87; D012967:Sodium Dodecyl Sulfate; D014364:Tryptophan; C028913:dodecyl sulfate; C031492:octanoic acid; D000212:Acyclovir