J. Biol. Chem., Vol. 255, Issue 16, 7621-7626, 08, 1980
Electron spin resonance studies of bovine plasma amine oxidase. Probing of the environment about the substrate-liberated sulfhydryl groups in the active site
H Zeidan, K Watanabe, LH Piette and KT Yasunobu
A series of nitroxide spin-labeled reagents have been employed to explore
the environment of the cysteine residues in bovine plasma amine oxidase.
When the enzyme was reduced by substrate or phenylhydrazine, 1 essential
sulfhydryl residue/subunit was liberated. This cysteine residue was reacted
then with the spin label 3-(maleimido-methyl)-
2,2,5,5-tetramethyl-1-pyrrolinyloxyl. The ESR spectra of the labeled enzyme
derivatives suggested that this essential sulfhydryl residue is located in
a pocket, whereas the nonessential sulfhydryl residues are probably located
near the surface. By varying the length of the nitroxide spin-labeled
N-ethylmaleimide derivatives, it was determined that the liberated
essential cysteine residues are in a restricted environment. The ESR
spectral data also suggested that the nitroxide radical and the essential
copper in the enzyme do not interact with one another. The effect of ionic
strength, pH, and urea denaturation on the environment of the essential
sulfhydryl residue were also investigated.