Interrelations of bioenergetic and sensory functions of the retinal proteins

Abstract

Rhodopsins are intrinsic membrane retinal-containing proteins composed of 7 hydrophobic alpha-helical transmembrane columns and hydrophilic sequences of various length connecting the helices and localized at N- and C-ends of the polypeptide. The chromophore (retinal) forms a Schiff base with a lysine residue in the middle part of the last alpha-helix. Absorption of a photon results in isomerization of retinal which gives rise to a conformational change in the protein moiety. Rhodopsins can be involved in two entirely different types of activities, i.e. ion pumping and photosensing. Recent observations concerning the pumping and sensory mechanisms allowed both these events to be explained in terms of one and the same unitary concept, which postulates the formation of a hydrophilic cleft in the hydrophobic part of the protein molecule as a crucial step in energy conservation and photosensing.

Differences in proton leak kinetics, but not in UCP3 protein content, in subsarcolemmal and intermyofibrillar skeletal muscle mitochondria from fed and fasted rats

“…Therefore, such a condition characterised by increased availability of fatty acid substrate with reduced ATP consumption could enhance the formation of ROS and oxidative damage in the cell [19]. Mild uncoupling by means of increased proton leak would counter this and avoid excess ROS production [20,21]. The different leak response to fasting in the two mitochondrial populations could be explained on the basis of their localisation.…”

Neurotoxic glutamate treatment of cultured cerebellar granule cells induces Ca2+‐dependent collapse of mitochondrial membrane potential and ultrastructural alterations of mitochondria

“…This can take place not only ruder exposure to exogenous GLU, but also during brain l~,ypoxia and ischemia. An exclusive role of mitochondria v as recently emphasized in cellular death where the step of mitochondrial permeability transitions seems to be crucial [22] makes the data on the loose mitochondrial coupling in intact cells under pathological conditions [23] very significant.…”

Complicated character of the M decay pH dependence in the D96N mutant is due to the two pathways of the M conversion

“…We suppose that there is an equilibrium between two forms of the M intermediate, differing in the state of the inward proton pathway. In Mope,~ a cleft permeable for water molecules as well as for small weak acids (azide) is formed in the cytosolfacing part of bR [10,14,21]. In the wild-type bacteriorhodopsin, the appearance of water near Asp-96 leads to a decrease a its pK [22][23][24][25].…”