Cd. Bhanumathy et As. Balasubramanian, EVIDENCE FOR A ZN2-BINDING SITE IN HUMAN SERUM BUTYRYLCHOLINESTERASE(), Biochemical journal, 315, 1996, pp. 127-131
Purified human serum butyrylcholinesterase after treatment with either
of the metal chelators EDTA or NaCN was able to bind to a Zn2+-chelat
e-Sepharose affinity column and was eluted from the column by EDTA or
imidazole. Prior EDTA treatment of the enzyme was essential for bindin
g to this affinity column. The enzyme could be labelled with Zn-65(2+)
after EDTA treatment of the enzyme. Diethylpyrocarbonate modification
of histidine residues in the EDTA-treated enzyme resulted in the abol
ition of both binding to the Zn2+-chelate-Sepharose column and labelli
ng by Zn-65(2+). Stoicheiometry of Zn-65(2+) binding indicated approxi
mately 0.85 mol of Zn2+/mol of subunit of the EDTA-treated enzyme. EDT
A or NaCN treatment resulted in the loss of thermal stability of the e
nzyme at 37 degrees C which could not be reversed by Zn2+. Whereas the
cholinesterase activity of butyryl cholinesterase was not affected by
EDTA, there was significant loss of its carboxypeptidase activity in
the presence of EDTA, and the loss could be reversed by added ZnCl2. T
hese results suggest the presence of a Zn2+-binding site on human seru
m butyrylcholinesterase and the involvement of histidine residues in t
he metal binding. The presence in human serum butyrylcholinesterase of
a sequence HXXE...H found in many known Zn2+-containing enzymes suppo
rts these findings.