TCA循环的英文版概述一定要英文版的,我是个英文文盲.怎么是在植物线粒体中的TCA循环呢？知不知道TCA循环的机理？如果能，用英语写一份给我，谢谢拉！

TCA循环的英文版概述一定要英文版的,我是个英文文盲.怎么是在植物线粒体中的TCA循环呢？知不知道TCA循环的机理？如果能，用英语写一份给我，谢谢拉！
TCA循环的英文版概述
一定要英文版的,我是个英文文盲.
怎么是在植物线粒体中的TCA循环呢？知不知道TCA循环的机理？如果能，用英语写一份给我，谢谢拉！

TCA循环的英文版概述一定要英文版的,我是个英文文盲.怎么是在植物线粒体中的TCA循环呢？知不知道TCA循环的机理？如果能，用英语写一份给我，谢谢拉！
TCA Cycle in Plant Mitochondria
The tricarboxylic acid (TCA) cycle in mitochondria catalyses the complete oxidation of organic acids to CO2 and the reduction of NAD(P) in the mitochondrial matrix and also the partial oxidation of organic acids leading to some CO2 release,NAD(P) reduction and the release of 4,5 and 6 carbon intermediates for biosynthesis in other parts of the cell.This pathway is made up of 9 major enzyme complexes which vary in native size from 120 kDa to 6,000 kDa.Most of our knowledge about these enzmyes comes from work in mammalian,yeast and bacterial systems,while in plants many of them have only received elementary levels of analysis.We have been specially interested in the two largest protein complexes pyruvate dehydrogenase complex (5,000 kDa) and 2-oxoglutarate dehydrogenase complex (3,000 kDa) which both catalyse the release of CO2 and the reduction of NAD to NADH.These enzymes contain a complex oligometric structure consisting of 3 different enzyme activities that combine to catalyse a single reaction with a number of bound intermediates handed from one enzyme to another.Both these enzymes are rapidly inhibited by the products of lipid peroxidation and this effect has been linked to the decline in respiration of heart tissues following ischaemia in mammals.We are now investigating the effect of oxidative stress in plants on the function of these enzymes.

The citric acid cycle [also known as the tricarboxylic acid (TCA) cycle, the Krebs cycle, or Szent-Györgyi-Krebs cycle (after Hans Adolf Krebs and Albert Szent-Györgyi who first determined t...

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The citric acid cycle [also known as the tricarboxylic acid (TCA) cycle, the Krebs cycle, or Szent-Györgyi-Krebs cycle (after Hans Adolf Krebs and Albert Szent-Györgyi who first determined the chemical intermediates and reaction sequence of the cycle)] is a series of enzyme-catalysed chemical reactions of central importance in all living cells that use oxygen as part of cellular respiration. In aerobic organisms, the citric acid cycle is part of a metabolic pathway involved in the chemical conversion of carbohydrates, fats and proteins into carbon dioxide and water to generate a form of usable energy. It is the third of four metabolic pathways that are involved in carbohydrate catabolism and ATP production, the other three being glycolysis and pyruvate oxidation before it, and electron transport chain after it.
The citric acid cycle also provides precursors for many compounds such as certain amino acids, and some of its reactions are therefore important even in cells performing fermentation.
Many of the enzymes in the TCA cycle are regulated by negative feedback from ATP when the energy charge of the cell is high. Such enzymes include the pyruvate dehydrogenase, citrate synthase, isocitrate dehydrogenase and alpha-ketoglutarate dehydrogenase. These enzymes, which regulate the first three steps of the TCA cycle, are inhibited by high concentrations of ATP. This regulation ensures that the TCA cycle will not oxidise excessive amounts of pyruvate and acetyl-CoA when ATP in the cell is plentiful. This type of negative regulation by ATP is by an allosteric mechanism.
Several enzymes are also negatively regulated when the level of reducing equivalents in a cell are high (high ratio of NADH/NAD+). This mechanism for regulation is due to substrate inhibition by NADH of the enzymes that use NAD+ as a substrate. This includes pyruvate dehydrogenase, citrate synthase, isocitrate dehydrogenase, alpha-ketoglutarate dehydrogenase, and malate dehydrogenase.
Calcium is used as a regulator. It activates pyruvate dehydrogenase, isocitrate dehydrogenase and oxoglutarate dehydrogenase.[1] This increases the reaction rate of many of the steps in the cycle, and therefore increases flux throughout the pathway.
Citrate is used for feedback inhibition, as it inhibits phosphofructokinase, an enzyme involved in glycolysis that makes fructose 1,6-bisphosphate), a precursor of pyruvate. This prevents a constant high rate of flux when there is an accumulation of citrate and a decrease in substrate for the enzyme.
Recent work has demonstrated an important link between intermediates of the citric acid cycle and the regulation of hypoxia inducible factors (HIF). HIF plays a role in the regulation of oxygen haemostasis and is a transcription factor which targets angiogenesis, vascular remodelling, glucose ulitisation, iron transport and apoptosis. HIF is synthesized consititutively and hydropxylation of at least one of two critical proline residues mediates their interation with the von Hippel Lindau E4 ubiquitin ligase complex which targets them for rapid degradation. This reaction is calalysed by prolyl 4-hydroxylases. Fumarate and succinate have been identified as potent inhibitors of prolyl hydroxylases thus leading to the stabilisation of HIF
Most of the body's catabolic pathways converge on the TCA cycle, as the diagram shows. Reactions that form intermediates of the TCA cycle in order to replenish them (especially during the scarcity of the intermediates) are called anaplerotic reactions.
The citric acid cycle is the third step in carbohydrate catabolism (the breakdown of sugars). Glycolysis breaks glucose (a six-carbon-molecule) down into pyruvate (a three-carbon molecule). In eukaryotes, pyruvate moves into the mitochondria. It is converted into acetyl-CoA by decarboxylation and enters the citric acid cycle.
In protein catabolism, proteins are broken down by protease enzymes into their constituent amino acids. These amino acids are brought into the cells and can be a source of energy by being funnelled into the citric acid cycle.
In fat catabolism, triglycerides are hydrolyzed to break them into fatty acids and glycerol. In the liver the glycerol can be converted into glucose via dihydroxyacetone phosphate and glyceraldehyde-3-phosphate by way of gluconeogenesis. In many tissues, especially heart tissue, fatty acids are broken down through a process known as beta oxidation which results in acetyl-CoA which can be used in the citric acid cycle. Sometimes beta oxidation can yield propionyl CoA which can result in further glucose production by gluconeogenesis in the liver.
The citric acid cycle is always followed by oxidative phosphorylation. This process extracts the energy (as electrons) from NADH and FADH2, oxidizing them to NAD+ and FAD, respectively, so that the cycle can continue. The citric acid cycle itself does not use oxygen, but oxidative phosphorylation does.
The total energy gained from the complete breakdown of one molecule of glucose by glycolysis, the citric acid cycle and oxidative phosphorylation equals about 36 ATP molecules. The citric acid cycle is called an amphibolic pathway because it participates in both catabolism and anabolism.

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