Nickel(II)‐binding constituents of human blood serum

Abstract

Studies were undertaken to investigate the Ni(II)‐binding properties of human blood serum and to identify the low‐molecular‐weight Ni(II)‐binding constitutents in the serum. Three Ni(II)‐binding fractions were obtained when labeled nickel chloride ( ⁶³ NiCl ₂ ) was added to the native serum. Of the total Ni(II), 95.7% was associated with albumin, 4.2% was bound to low‐molecular‐weight components, and a small fraction, usually less than 0.1%, was associated with a high‐molecular‐weight protein that was eluted in the void volume of Sephadex G‐150. Amino acids were shown to be responsible for the low‐molecular‐weight Ni(II)‐binding fraction and L‐histidine was found to be the main Ni(II)‐binding amino acid in human blood serum. Compared with albumin, L‐histidine was shown to possess a greater affinity for Ni(II). Ni(II)‐binding to human albumin became evident only when no more L‐histidine was available. Since the concentration of albumin is much higher than the concentration of L‐histidine in normal serum, most of the added Ni(II) was associated with albumin. The equilibria between Ni(II)‐L‐histidine and Ni(II)‐albumin may facilitate the transport of Ni(II) between blood and tissues.