The globule diameter and some electron and conformational properties of the flavoprotein fragment of mitochondrial NADH dehydrogenase studied by fluorescence spectroscopy

The globule dimensions and some electron and conformational properties of t he flavoprotein (peripheral) fragment of the mitochondrial NADH dehydrogena se were determined by the time-resolved, phase-modulating, and polarization fluorescence spectroscopies, as well as correlated confocal microscopy. Th e rotational and the diffusion (translocation) diameters of the protein fra gment were shown to be no less than 44 Angstrom and similar to 72 Angstrom, respectively. The diameter of protomitochondrial particles from the bovine heart, which were used for the isolation of the fraction of peripheral fra gments, was no less than 2300 Angstrom. The fluorescence from tryptophan an d flavin fluorophores in the fragment is strongly quenched by iron of the i ron-sulfur clusters, which suggests that a strong electron-vibrational inte raction of iron with Trp residues and flavin takes place. An overlapping of the electron clouds of iron-sulfur clusters, Trp residues, and flavin is l ikely to facilitate the electron transfer through the protein. The heat ina ctivation of the enzyme was accompanied by neither its substantial conforma tional changes, nor a considerable release of iron ions from the clusters l ocated near the Trp residues.