Adsorption of small molecules to bovine serum albumin studied by the spin-probe method.

A spin-probe technique is used for quantitative EPR studies of adsorption of small molecules on globular proteins, of the rigidity of their binding to the protein and of the polarity of the environment. In the case of bovine serum albumin it is shown that nitroxyl radical (2, 2, 6, 6-tetramethyl-4-oxy-1-oxyl-piperidine)-stearate (I) has an adsorption behaviour similar to that of the fatty acids, nitroxyl radical (2, 2,4, 4-tetramethyl-1, 2, 3, 4-tetrahydro-5, 6-benzo-gamma-carboline-3-oxyl) (II) to that of the tryptophan molecule. Radical I rotates relative to the protein molecule, while Radical II is rigidly bound to the protein.