Tabata M, Sarkar B
Research Institute, Hospital for Sick Children, Toronto, Ontario, Canada.
J Inorg Biochem. 1992 Feb 1;45(2):93-104. doi: 10.1016/0162-0134(92)80003-e.
The kinetics and mechanism for Ni(II)-transfer of the native sequence tripeptide, L-aspartyl-L-alanyl-L-histidine-N-methylamide (AAHNMA), representing the Ni(II)-transport site of human serum albumin (HSA) and L-histidine (L-His) was studied in forward and reverse reactions in the pH range 6.5 to 9.0 at I = 0.2 and 25 degrees C. For the Ni(II)-transfer from Ni(II)-(L-His)2 to native sequence peptide, the rate-determining step is the formation of a mixed-ligand complex of NiH-1AB by deprotonation of peptide nitrogen from NiAB where A and B denote the anionic forms of AAHNMA and L-His, respectively. For the Ni(II)-transfer from Ni(II)-peptide to L-His, the rate-determining step is a bond breaking between Ni(II) and peptide nitrogen to form NiH-1A by protonation to a peptide nitrogen of NiH-2A. The equilibrium constants for the metal-transfer reaction of MH-2A + 2HB in equilibrium MB2 + A (A = Ni(II), Cu(II] were 10(3.29) and 10(0.78) for Ni(II) and Cu(II), respectively. NiB2 is 324 times as stable as CuB2. Furthermore, the ratio of Ni(II)/Cu(II) in the rate constants for the reaction of MB2 with A was found to be 2.8 x 10(-4). Thus, despite the similarities of Cu(II) and Ni(II) in the metal-binding sites of HSA and in reaction mechanism, Ni(II)-(L-His)2 complex is so stable thermodynamically and kinetically, compared to the Cu(II)-(L-His)2 complex, that Ni(II) is hardly transferred from Ni(II)-(L-His)2 to native sequence peptide. These findings may support specificities in the Ni(II)-transfer, its organ distribution, and its excretion through urine in vivo.
研究了代表人类血清白蛋白（HSA）镍（II）转运位点的天然序列三肽L-天冬氨酰-L-丙氨酰-L-组氨酸-N-甲基酰胺（AAHNMA）和L-组氨酸（L-His）在pH值6.5至9.0、离子强度I = 0.2及25℃条件下，正逆反应中镍（II）转移的动力学及机制。对于镍（II）从镍（II）-（L-His）₂转移至天然序列肽的过程，速率决定步骤是肽氮从镍AB去质子化形成镍H-1AB混合配体络合物，其中A和B分别表示AAHNMA和L-His的阴离子形式。对于镍（II）从镍（II）-肽转移至L-His的过程，速率决定步骤是镍（II）与肽氮之间的键断裂，通过质子化至镍H-2A的肽氮形成镍H-1A。金属转移反应MH-2A + 2HB ⇌ MB₂ + A（A = Ni(II)，Cu(II)）的平衡常数，对于镍（II）和铜（II）分别为10³.²⁹和10⁰.⁷⁸。镍B₂的稳定性是铜B₂的324倍。此外，发现MB₂与A反应的速率常数中镍（II）/铜（II）的比值为2.8×10⁻⁴。因此，尽管铜（II）和镍（II）在HSA的金属结合位点及反应机制上存在相似性，但与铜（II）-（L-His）₂络合物相比，镍（II）-（L-His）₂络合物在热力学和动力学上都非常稳定，以至于镍（II）几乎不会从镍（II）-（L-His）₂转移至天然序列肽。这些发现可能支持了镍（II）转移、其器官分布以及在体内通过尿液排泄的特异性。
