FLEXIBILTY OF IMMUNOGLOBULIN G MOLECULES AS ESTABLISHED BY FLUORESCENT POLARISATION MEASUREMENTS

The fluorescent properties of 1-dimethylaminonaphthalene-5-sulfonyl (DNS) conjugates of human and rabbit immunoglobulins G (HGG and RGG), have been shown to be different from those of bovine serum albumin (BSA) and ovalbumin (OA). The former group of conjugates revealed a shorter lifetime of the excited state (τ=7·3 nsec), a lower quantum yield, and a longer wavelength of fluorescence maximum (543 nm). The latter group showed τ=12·1 nsec, several times higher shorter wavelength (523 nm) of fluorescence maximum. The rotational relaxatin time (ρ{variant}h) of the DNS-HGG conjugate obtained by measuring the fluorescence polarisation was found to be 60 nsec. This value is several times lower than calculated on the assumption that the molecule is rigid (ρ{variant}h=220 nsec). This points to the pronounced flexibility of HGG molecule. The above difference in behaviour of two groups of protein dansyl conjugates might be due to two causes. Firstly, the optical properties of DNS residues can depend on the particular amino acid to which the DNS group has become attached. This possibility is substantiated by our experiments that showed the differences in fluorescence properties of DNS derivatives of various amino acids. Secondly, the properties of the DNS residues might depend on the more or less hydrophobic character of their environment as shown, in particular, by our evidence. © 1969.