Measurement of the interaction of quaeous copper(II) with a model amyloid-beta protein fragment - Interference from buffers

作者：Benn Michael H; Rauk Arvi; Swaddle Thomas W^*

来源：Canadian Journal of Chemistry, 2011, 89(12): 1429-1444.

DOI：10.1139/V11-101

• N-alpha-dihydrourocanylhistamine complexes with copper(II)
• amyloid-beta complexes with copper(II)
• Tris buffer complexes with copper(II)
• buffer interferences in biochemical measurements

For the formation of a complex of Cu(2+) with the amyloid-beta (A beta) proxy N-alpha-dihydrourocanylhistamine (L) in unbuffered aqueous solution (pH similar to 5.7, 25.0 degrees C), UV spectrophotometric measurements give a stability constant of 3.8 x 10(5) L mol(-1). This stability constant is within the lower limit of the range of stability constants reported in the literature for complexes of A beta with Cu(2+) - as expected, in view of the smaller number of coordination sites in L. Computer modeling indicates that the Cu(2+)-L complex is CuL(H(2)O)(2)(2+), with terdentate L bound to Cu(2+) via two N pi, atoms and the O atom of the peptide link. Attempts to make stability constant measurements for Cu(2+) with L in aqueous solution buffered with Tris/TrisH(+)/ClO(4)(-) to pH near 7.2 were unsuccessful because the Tris base when in large excess over CuL(2+) promoted its dissociation to Cu(2+) + L by scavenging free Cu(2+) as Cu(Tris)(TrisH(-1))(+), or when in roughly equimolar concentrations formed a ternary adduct, CuL(Tris)(2+). The interactions of Cu(2+) with Tris buffer were re-examined spectrophotometrically and with the aid of computations that show that the most stable Cu(2+)-Tris complexes are the syn- and anti-isomers of Cu(Tris)(2)(2+), but in the experimental pH ranges these are present as Cu(Tris)(TrisH(-1))(+). Since Cu(2+)(aq) is strongly complexed by almost any base capable of forming a buffer system with near-physiological pH, stability constants reported for Cu(2+)-A beta complexes in any buffer solution should be regarded with skepticism unless interactions of the buffer with Cu(2+) and with CuA beta(2+) are taken quantitatively into account. Moreover, in vivo, biological buffers will reduce the physiological importance of A beta-Cu(2+) complexes by competing with A beta for Cu(2+).

• 出版日期2011-12