Fluorescent styryl dyes as probes for Na,K-ATPase reaction mechanism: significance of the charge of the hydrophilic moiety of RH dyes

The structure of the styryl-based RH dyes regulates the fluorescence response of Na,K-ATPase towards phosphorylation. The net charge of the dye molecule is a critical factor for determining the sensitivity and the spectral properties of the dyes response to phophorylation. Computer modeling of dyes with the same chromophore structure reveals that the absorption maximum of the zwitterionic dyes is blue-shifted and the quantum yield of these dyes is higher than that for the positively charged dyes. The electrostatic interactions between the hydrophilic headgroup of the dye and the enzyme change the net charge of the dye molecule.