STUDY OF SOME PHYSICOCHEMICAL PROPERTIES OF THE NEUROTOXIC COMPLEX AND ITS COMPONENTS FROM THE VENOM OF BULGARIAN SAND VIPER, VIPERA-AMMODYTES-AMMODYTES .1. LUMINESCENCE OF TRYPTOPHAN RESIDUES

A series of parameters of intrinsic fluorescence and phosphorescence of the viper neurotoxic complex from Vipera ammodytes ammodytes venom and its isolated acidic (A) and basic (B) protein components was measured at a wide range of conditions (pH from 2.0 to 12.0, temperature from 10 to 70°C and at liquid nitrogen temperature). Three tryptophanyls in isolated component B (phospholipase A) at neutral pH show a fluorescence spectrum which can be described as the sum of two almost equal contributions: that of buried chromophores (spectral maximum at λm approx. 330 nm, halfwidth Δλ β48 nm) and that of chromophores exposed to the rapidly relaxing solvent (λm approx. 350 nm, Δλ β 61 nm). Two tryptophanyls in the component A at neutral pH possess the monocomponent fluorescence spectrum (λm approx. 351, 5 nm, Δλ β 62 nm) belonging to chromophores exposed to free water. Very low values of fluorescence quantum yield for both the components (approx.0.08) suggest the localization near the tryptophanyls of some extra quenching groups. Fluorometric titration shows that in component A this quenching group cannot be histidine, or amino groups. Deprotonation of α- and ε{lunate}-aminogroups in component B give rise either to a set of structural changes of the protein or contact quenching of tryptophanyl fluorescence. The whole neurotoxic complex shows luminescence properties very different from those of isolated components A and B. Its fluorescence parameters (λm = 335 nm, Δλ = 50.5 nm, quantum yield 0.11) revela that all tryptophanyls are buried. It is possible, however, that the environment of chromophores in the complex is to some extent more mobile than that of typical buried tryptophanyls of globular proteins. © 1979.