[Use of triplet state exchange disactivation phenomenon for the study of structure and electron conductivity of proteins].

A method for studying protein structure and estimating its electron conducting properties is proposed. The method is based on the kinetic recording of exchange quenching triplet labels and probes phosphorescence by chromophores or paramagnetic centres. It is shown that different types of exchange interactions (spin exchange, exchange energy transfer) between centres with distance R are described approximately by an equation (I = I0 exp-2R/L) where L changes from 0.7 A (absence of electron coupling--system of type I) to 6.5 A (strong electron coupling--system of type II). I (sec-1) corresponds to exchange energy transfer rate constant or exchange integral in the case of spin exchange. Life-times of excited triplet state eosin-isotiocionate labels connected with the terminal NH2-groups of the following preparations were measured by the method of kinetic phosphorescence decay recording: human oxyhemoglobin, methemoglobin, F- and CN-methemoglobin, metmyoglobin, F- and CN-metmyoglobins. The influence of lysozyme of the nitroxyl spin label bound to His-15 group on the phosphorescence spectrum was investigated. The analysis of our and literature data on the exchange interactions between the centres localized on the protein with known structure (hemoglobin, myoglobin, lysozyme, carboangidrase, bacterial ferredoxin) permit us to conclude that in the examined cases the experimental values correspond to model systems of type I and are different from the dependence in systems of type II by 5--15 order. This allows us to use equation (I) for estimation of the distances between the centres on proteins.