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Protons tunnel across a series of hydrogen bonds between hydronium ions and water molecules.. The Grotthuss mechanism (also known as proton jumping) is a model for the process by which an 'excess' proton or proton defect diffuses through the hydrogen bond network of water molecules or other hydrogen-bonded liquids through the formation and concomitant cleavage of covalent bonds involving ...
Histidine ball and stick model spinning. Histidine (symbol His or H) [2] is an essential amino acid that is used in the biosynthesis of proteins.It contains an α-amino group (which is in the protonated –NH 3 + form under biological conditions), a carboxylic acid group (which is in the deprotonated –COO − form under biological conditions), and an imidazole side chain (which is partially ...
Histidine is thus able to act as a powerful general base, activating the serine nucleophile. The histidine base aids the first leaving group by donating a proton, and also activates the hydrolytic water substrate by abstracting a proton as the remaining OH − attacks the acyl-enzyme intermediate.
Specifically, when the histidine is protonated, the His residue can form a hydrogen bond with the substrate's carbonyl oxygen, which shifts electron density away from the oxygen and makes it more susceptible to nucleophilic attack by hydride. This promotes the binding of malate dehydrogenase to these substrates.
An electron transport chain (ETC [1]) is a series of protein complexes and other molecules which transfer electrons from electron donors to electron acceptors via redox reactions (both reduction and oxidation occurring simultaneously) and couples this electron transfer with the transfer of protons (H + ions) across a membrane.
Continuing with the T4 lysozyme example, a titration curve is obtained through observation of a shift in the C2 proton of histidine 31 (Figure 5). Figure 5 shows the shift in the titration curve between the wild-type and the mutant in which Asp70 is Asn. The salt bridge formed is between the deprotonated Asp70 and protonated His31.
The final electron acceptor oxygen is reduced to water in this step. Both the direct pumping of protons and the consumption of matrix protons in the reduction of oxygen contribute to the proton gradient. The reaction catalyzed is the oxidation of cytochrome c and the reduction of oxygen:
Anaerobic cellular respiration and fermentation generate ATP in very different ways, and the terms should not be treated as synonyms. Cellular respiration (both aerobic and anaerobic) uses highly reduced chemical compounds such as NADH and FADH 2 (for example produced during glycolysis and the citric acid cycle) to establish an electrochemical gradient (often a proton gradient) across a membrane.