[Interaction of the toxic plant protein--ricin, with model membranes. A fluorescence method of study]. / Vzaimodeistvie rastitel'nogo toksichnogo belka--ritsina s model'nymi membranami. Issledovanie metodom fluorestsentsii.

The fluorescence method has been used to investigate ricin and its isolated subunits interaction with some model membranes. Three liposome types were used as a model of biological membrane: 1) liposomes constructed from lecithin and cholesterol (9:1, M:M) 2) from ganglioside receptors GM1 and 3) from the mixture of GM1, lecithin and cholesterol (1:9:1). Interaction of the protein with liposome evokes changes in the parameters of both intrinsic protein fluorescence and fluorescence of the covalently bound dansyl. Binding constants were calculated from a decrease of the intrinsic fluorescence intensity as well as from the changes in the dansyl rotation anisotropy. Measurements were carried out at neutral and acidic pH. There was good correlation of the results obtained by different methods. It was shown that association constants were different for intact ricin and its subunits. The constants also depend on liposome composition and pH of the solution. The present study has demonstrated that interaction of ricin with liposome is accounted for not only by receptor centers but also by other hydrophobic regions of ricin that are inaccessible in the native toxin and may represent the region of the subunits interaction.

[Features of the structure of catalytic subunits of toxins, inhibiting protein synthesis. I. The effect of pH and interaction with the B-chain of ricin]. / Osobennosti struktury kataliticheskikh sub''edinits toksinov, ingibiruiushchikh belkovyi sintez. I. Vliianie pH, vzaimodeistvie s B-tsep'iu ritsina.

A comparative study of gelonin and A-chains of ricin, mistletoe lectin I and diphtheria toxin was undertaken. The effect of pH was studied on: a) the conformation of the proteins under study using intrinsic fluorescence; b) interaction of these proteins with ricin B-chain using gel-filtration. Structural stability of the proteins was assessed according to denaturing action of guanidine hydrochloride and temperature, and localization of tryptophan residues was determined using fluorescence quenching by I-, Cs+ and acrylamide. All investigated proteins were shown to undergo the conformational changes when a environment became acidic. In comparison with an intact protein--gelonin, the A-chains of ricin, a mistletoe lectin and a diphtheria toxin are less stable. At pH less than 5.0 tryptophan residues became more accessible to quencher and a positive charge of the surrounding area increases (in the case of gelonin it is negatively charged). No reliable interaction of a ricin B-chain with both gelonin and A-chain of diphtheria toxin was observed. The interaction of a ricin B-chain with a A-chain of mistletoe lectin I is weaker than that with ricin A-chain and is practically pH-independent.