Evidence for protein self-association induced by excluded volume. Myoglobin in the presence of globular proteins.

The fluorescence polarization of fluorescent derivatives of hemoglobin and myoglobin was measured as a function of the concentration of added polymers (PEG-6 000, PEG-20 000) and globular proteins (lysozyme, ribonuclease A, beta-lactoglobulin). The results indicated that the effective size and shape of 1-anilino-9-naphthalene sulfonate myoglobin are unaltered in the presence of up to 25 g/dl poly(ethylene glycol), whereas they are significantly altered in the presence of comparable concentrations of other proteins. The results are consistent with the hypothesis that in the presence of high concentrations of added protein, 1-anilino-9-naphthalene sulfonate myoglobin self-associates to form a dimer similar in size and shape to 1-anilino-9-naphthalene sulfonate hemoglobin.