<title>Tryptophan phosphorescence as a monitor of flexibility of membrane proteins in cells</title>

Abstract

Method of room temperature tryptophan phosphorescence (RTTP) has been used to study slow intramolecular equilibrium motions in membrane proteins. The conventional home-made instruments were employed for measurement of RTTP kinetic and spectral parameters. Objects of the investigation were suspensions of human erythrocyte membranes, different animal and plant cells. On rat gepathocytes it has been shown that membrane proteins in composition of subcellular structures and native cells are able to the RTTP with tens and hundreds milliseconds lifetimes. An overwhelming part of soluble proteins of cytoplasm, karyoplasm and mitochondrial matrix has not capability to RTTP with lifetimes above 1 ms. It is concluded that unlike membrane proteins soluble proteins as a rule are characterized by motions of protein structure with intensive low frequency and large amplitude, that leads to pronounced quenching of their RTTP. In the case of membrane proteins, which are capable of phosphorescence in a millisecond range, the flexibility of the chromophores environment decreases. These results indicate that RTTP method gives the unique possibility to investigate dynamical structure of membrane proteins without their preliminary isolation from cells. The data on membrane proteins intramolecular dynamics in composition of cells at the action of biological active substances in physiological concentrations--Concavalin A, nerve growth factor, epidermal growth factor, 24-epibrassinosteroid received by the phosphorescent method are presented.