Enzyme: Hexokinase

Reaction: Phosphorylation

Free Energy Change:

•Standard Conditions: -4.0 kcal/mol

•Physiological Conditions: -8.0 kcal/mol irreversible

Enzyme: Phosphoglucose isomerase

Reaction: Aldose to Ketose Isomerisation

Free Energy Change:

•Standard Conditions: +0.4 kcal/mol

•Physiological Conditions: -0.6 kcal/mol reversible

Enzyme: Phosphofructokinase

Reaction: Phosphorylation

Free Energy Change:

•Standard Conditions: -3.4 kcal/mol

•Physiological Conditions: -5.3 kcal/mol irreversible

Enzyme: AldolaseReaction: Aldol CleavageFree Energy Change:

•Standard Conditions: +5.7 kcal/mol •Physiological Conditions: -0.3 kcal/mol reversible

Enzyme: Triose phosphate isomeraseReaction: Ketose to Aldose IsomerisationFree Energy Change

•Standard Conditions: +1.8 kcal/mol •Physiological Conditions: -+0.6 kcal/mol reversible

Enzyme: Glyceraldehyde 3-phosphate dehydrogenaseReaction: Coupled Oxidation & PhosphorylationFree Energy Change

•Standard Conditions: +1.5 kcal/mol

•Physiological Conditions: -0.4 kcal/mol reversible

Enzyme: Phosphoglycerate kinaseReaction: DephosphorylationFree Energy Change:

•Standard Conditions: -4.5 kcal/mol •Physiological Conditions: +0.3 kcal/mol reversible

Enzyme: PhosphoglyceromutaseReaction: Phosphate group shiftFree Energy Change:

•Standard Conditions: +1.1 kcal/mol

•Physiological Conditions: +0.2 kcal/mol reversible

Enzyme: Pyruvate kinaseReaction: DephosphorylationFree Energy Change:

•Standard Conditions: -7.5 kcal/mol

•Physiological Conditions: -4.0 kcal/mol irreversible

Enzyme: Lactate dehydrogenaseReaction: ReductionFree Energy Change:

•Standard Conditions: kcal/mol

•Physiological Conditions: kcal/mol reversible

Enzyme: Enolase

Reaction: Dehydration

Free Energy Change:

•Standard Conditions: +0.4 kcal/mol

•Physiological Conditions: -0.8 kcal/mol reversible

Enzyme: Citrate synthaseReaction: CondensationAcetyl CoA condenses with oxaloacetate first,to form citryl CoA. Then citryl CoA is hydrolyzed to citrate and CoA. Prosthetic group: No

Enzyme: AconitaseReaction: DehydrationCitrate is isomerized to isocitrate by this first dehydration and yields cis-aconitate as an intermediate. Prosthetic group: Fe-S

Enzyme: AconitaseReaction: HydrationHydration of cis-aconitate gives the interchange of H atom and OH group from the step 2. Prosthetic group: Fe-S

Enzyme: Isocitrate dehydrogenaseReaction: Oxidative decarboxylationDehydrogenation of isocitrate occurs and yields oxalosuccinate as an intermediate.Then CO2 leaves to have alpha-ketoglutarate.This reaction gives NADH. Prosthetic group: No

Enzyme: alpha-Ketoglutarate dehydrogenase complexReaction: Oxidative decarboxylationThis mechanism is almost as same as the reaction of the oxidative decarboxylation of pyruvate to acetyl CoA by pyruvate dehydrogenase complex. This reaction gives one NADH. Prosthetic group: Lipoic acid, FAD, TPP

Enzyme: Succinyl CoA synthetaseReaction: Substrate-level phosphorylationThe thioester bond of succinyl and CoA is an energy rich bond. Thus only this step gives a high-energy phosphate compound,GTP from the couple reactions of the thioester bond cleavage and the phosphorylation of GDP. Prosthetic group:No

Enzyme: Succinate dehydrogenaseReaction: OxidationThe two hydrogens of succinate leave to an acceptor, FAD. Then this reaction yields fumarate and FADH2. Prosthetic group: FAD & Fe-S

Enzyme: Malate dehydrogenaseReaction: OxidationMalate is dehydrogenated to form oxaloacetate. The hydrogenacceptor is NAD. So this reaction yields NADH. Prosthetic group: No

Enzyme: Fumarase

Reaction: HydratationFumarate is hydrated to give Malate.

Prosthetic group: No

                                                                                                        

                                                                                                                                                

                    A typical representation of an electron transport chain. Images from Purves et al., Life: The Science of Biology, 4th Edition, by Sinauer Associates (www.sinauer.com) and WH Freeman (www.whfreeman.com), used with permission.During chemiosmosis in eukaryotes, H+ ions are pumped across an organelle membrane into a confined space (bounded by membranes) that contains numerous hydrogen ions. The energy for the pumping comes from the coupled oxidation-reduction reactions in the electron transport chain. Electrons are passed from one membrane-bound enzyme to another, losing some energy with each tansfer (as per the second law of thermodynamics). This "lost" energy allows for the pumping of hydrogen ions against the concentration gradient (there are fewer hydrogen ions outside the confined space than there are inside the confined space). The confined hydrogens cannot pass back through the membrane. Their only exit is through the ATP synthesizing enzyme that is located in the confining membrane. As the hydrogen passes through the ATP synthesizing enzyme, energy from the enzyme is used to attach a third phosphate to ADP, converting it to ATP.