![]() ![]() Being ‘voltage-gated’ means that it can sense voltage, specifically the electrical potential difference across a cell membrane. The protein at the focus of this chapter is the voltage-gated proton channel, H V1. ![]() ROS production by NOX5 mediates motility Optimize pH i for NOX volume regulation Īlkaline pH i triggers capacitation Prevent NOX self-inhibition at high potentials Optimize pH of airway surface fluid CO 2 extrusion Involvement of H V1 in human health is extensive, but beyond the scope of this review. An astonishing variety of functions have been identified in these phylogenetically disparate species, many of which are listed in table 1. To date, only one gene per species has been found, although, in several cases, truncated isoforms have been identified. Subsequently, proton currents have been identified in cells from 15 species, and HVCN1 genes (that code for H V1) in another 11 species have been confirmed by expression in heterologous systems and voltage clamp. Nearly a quarter of a century later, the gene for voltage-gated proton channels was finally identified. Proof of the existence of H V1 was produced a decade later by Thomas and Meech with their 1982 voltage-clamp study of snail neurons. Its existence was first postulated in 1972 by Hastings and co-workers, who proposed that it triggered the flash in bioluminescent dinoflagellates, a role that was recently confirmed. H V1 is a unique ion channel, a membrane protein that allows protons (H +) but no other ions to cross cell membranes. The focus of this review is how the voltage-gated proton channel, H V1, senses voltage and pH. We propose a ‘counter-charge’ model for pH sensing in which electrostatic interactions within the protein are selectively disrupted by protonation of internally or externally accessible groups. For this purpose their p K a needs to be within the operational pH range. ![]() The mechanism of pH sensing appears to involve titratable side chains of particular amino acids. Currently, it is hypothesized that membrane potential is sensed by permanently charged arginines (with very high p K a) within the protein, which results in parts of the protein moving to produce a conduction pathway. Here we summarize what is known about the way these proteins sense the membrane potential and the pH inside and outside the cell. Their activity has electrical consequences and also changes the pH on both sides of the membrane. Consequently, these proteins behave like rectifiers, conducting protons out of cells. In all cells, their function requires that they open and conduct current only under certain conditions, typically when the electrochemical gradient for protons is outwards. They are found in diverse species, from unicellular marine life to humans. The return flow of proton down their electrochemical gradient through the enzymatic complex is responsible for the activation of ATPase which drives the synthesis of ATP from ADP and phosphate.Voltage-gated proton channels are unique ion channels, membrane proteins that allow protons but no other ions to cross cell membranes. This force drives protons across the membrane towards the mitochondrial matrix. The pH gradient and the proton concentration gradient across the inner membrane built a proton motive force. Thus a pH gradient is generated across the inner mitochondrial membrane. The pH of the outer surface of inner mitochondrial membrane lowers considerably due to the concentration of net positive charge. The unidirectional flow of protons towards the outer side results in the accumulation of protons in the intermembrane space. Similarly, FADH 2 also transports pairs of protons into the intermembrane space. Reduced NAD released from Krebs cycle when enter in the electron transport system transports three pairs of protons across the inner mitochondrial membrane to the intermembrane space. The respiratory chain is oriented in such a way that the electrons move in an inward direction and protons flow in an outward direction. The inner mitochondrial membrane is permeable to water but impermeable to protons except at the points where the respiratory chain and ATP synthase are located. ![]()
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