High-Energy Phosphate Bond

PhenylPhosphorothioa.te Esters. These are the most widely used OP iasecticides and iacorporate pseudoanhydride high energy phosphate bonds between phosphoric acid and phenols that are present ia the activated P=0 state. 

Two and twelve moles of ATP are produced, respectively, per mole of glucose consumed in the glycolytic pathway and each turn of the Krebs (citrate) cycle. In fat metaboHsm, many high energy bonds are produced per mole of fatty ester oxidized. Eor example, 129 high energy phosphate bonds are produced per mole of palmitate. Oxidative phosphorylation has a remarkable 75% efficiency. Three moles of ATP are utilized per transfer of two electrons, compared to the theoretical four. The process occurs via a series of reactions involving flavoproteins, quinones such as coenzyme Q, and cytochromes. 

Mitochondria Mitochondria are organelles surrounded by two membranes that differ markedly in their protein and lipid composition. The inner membrane and its interior volume, the matrix, contain many important enzymes of energy metabolism. Mitochondria are about the size of bacteria, 1 fim. Cells contain hundreds of mitochondria, which collectively occupy about one-fifth of the cell volume. Mitochondria are the power plants of eukaryotic cells where carbohydrates, fats, and amino acids are oxidized to CO9 and H9O. The energy released is trapped as high-energy phosphate bonds in ATR... 

The transport of each COg requires the expenditure of two high-energy phosphate bonds. The energy of these bonds is expended in the phosphorylation of pyruvate to PEP (phosphoenolpyruvate) by the plant enzyme pyruvate-Pj dikinase the products are PEP, AMP, and pyrophosphate (PPi). This represents a unique phosphotransferase reaction in that both the /3- and y-phosphates of a single ATP are used to phosphorylate the two substrates, pyruvate and Pj. The reaction mechanism involves an enzyme phosphohistidine intermediate. The y-phosphate of ATP is transferred to Pj, whereas formation of E-His-P occurs by addition of the /3-phosphate from ATP ... 

The charging of the tRNA molecule with the aminoacyl moiety requires the hydrolysis of an ATP to an AMP, equivalent to the hydrolysis of two ATPs to two ADPs and phosphates. The entry of the aminoacyl-tRNA into the A site results in the hydrolysis of one GTP to GDP. Translocation of the newly formed pep-tidyl-tRNA in the A site into the P site by EF2 similarly results in hydrolysis of GTP to GDP and phosphate. Thus, the energy requirements for the formation of one peptide bond include the equivalent of the hydrolysis of two ATP molecules to ADP and of two GTP molecules to GDP, or the hydrolysis of four high-energy phosphate bonds. A eukaryotic ribosome can incorporate as many as six amino acids per second prokaryotic ribosomes incorporate as many as 18 per second. Thus, the process of peptide synthesis occurs with great speed and accuracy until a termination codon is reached. 

Use of High-Energy Phosphate Bonds During Translation 60... 

USE OF HIGH-ENERGY PHOSPHATE BONDS DURING TRANSLATION... 

How many high-energy phosphate bonds are required for the synthesis of a protein from amino acids during translation ... 

For reactions that make PP (pyrophosphate), the PP, is rapidly hydrolyzed to 2 P in the cell, so we ll consider the formation of PP to use 2 high-energy-phosphate bonds. 

Oxidative Phosphorylation Electron transfer through the cytochrome system liberating free energy which is transformed into high-energy phosphate bonds. [NIH]... 

During p-globin synthesis in normal reticulocytes the sequoice his-atg-pro occurs at position 165-167. How many high-energy phosphate bonds are required to insert these 3 amino acids into the p-globin polypeptide during translation ... 

An intriguing use of the oxidative potential stored in thianthrene radical ion(l-l-) is provided by the formation of high-energy phosphate bonds. Thus, the interaction of adenosine-5 -phosphate (AMP) and orthophos-phoric acid, each as their ammonium salts, with two equivalents of thi-... 

The formation of 1,3-bisphosphoglycerate involves the synthesis of a high-energy phosphate bond as the aldehyde of glyceraldehyde 3-phosphate is oxidized to a carboxylic acid and then phosphorylated by reaction with inorganic phosphate. 

This is an example of substrate-level phosphorylation, ie, the creation of a high-energy phosphate bond through a chemical reaction rather than via oxidative phosphorylation (see Chapter 7). 

Proteins are costly to the cell, requiring hydrolysis of five high-energy phosphate bonds per amino acid incorporated. 

ATP Regarded as Store House of Energy Adenosine triphosphate (ATP) in a nucleotide consists of purine base adenine, a pentose sugar ribose and three molecules of phosphate. It contains two oxygen to phosphorus bonds between two phosphate units. These phosphorus bonds are called high energy phosphatic bonds. 

For the phosphotransferase system there is no problem in identifying the energy source for the establishment of the thermodynamic potential gradient. It is apparent that a high-energy phosphate bond in phospho-enol-pyruvate is the immediate source of the energy responsible for the vectorial translocation of the sugar molecule across the membrane (17). 

Enolase catalyzes the dehydration of 2-phosphoglycerate to form phospho-enolpyruvate (PEP). This reaction converts the low-energy phosphate ester bond of 2-phosphoglycerate into the high-energy phosphate bond of PEP. 

The pyrophosphate from the pyruvate-P dikinase is rapidly degraded so that, overall, the net price the plant pays for operation of this C02 pump is the hydrolysis of two high-energy phosphate bonds for every molecule of C02 transported ... 

Note that the hydrolysis of two high-energy phosphate bonds in ATP provides the energy source for the reaction. The inorganic pyrophosphate, PPi, is subsequently broken down to two phosphate ions by inorganic pyrophosphatase. The action of this enzyme means that very little PPi remains in the cell, making the synthesis of the fatty acyl-CoA favored. This is an example of metabolic coupling, the process whereby a thermodynamically unfavored reaction is allowed because it shares an intermediate (in this case PPO with a favored one. 

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