J. Biol. Chem., Vol. 256, Issue 5, 2280-2283, 03, 1981
Esterase activity of hemoglobin. Differences between HB A and HB S
D Elbaum and RL Nagel
The hydrolysis of p-nitrophenyl acetate (p-NPA) is catalyzed by many
proteins. We have observed that oxyhemoglobin A also exhibits esterase
activity with a rate intermediate between that of bovine albumin and
carbonic anhydrase. Kinetic studies of this reaction revealed that the rate
of hydrolysis of p-NPA in the presence of oxy Hb S was approximately 2
times slower than that of oxy Hb A. There is general agreement that the
catalytic effect of peptides and proteins on the hydrolysis of p-NPA is
mediated by histidines. Oxy Hb Deer Lodge (His beta 2 leads to Arg)
hydrolyzes p-NPA at a rate approaching that of oxy Hb S. Oxy Hb F, in turn,
exhibits a rate indistinguishable from that of oxy Hb A. The effect of
2,3-diphosphoglyceric acid on the reaction is consistent with the
participation of His beta 2 in this catalytic effect. The pH dependence of
the reaction and studies with free amino acids also lend support to the
involvement of a histidine residue. These results point to subtle
conformational differences between oxy Hb S and oxy Hb A in solution,
probably involving His beta 2 and/or its microenvironment. The catalytic
hydrolysis of p-NPA can be considered a useful probe of conformational
states of macromolecules.
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