Three-carbon phosphates

Step 4. Cleavage of Fructose-1,6-Bisphosphate into Three-Carbon Phosphates The reaction is... 

Fructose-1,6-bisphosphate is split into two three-carbon phosphate isomers dihydroxyacetone phosphate and glyceraldehyde-3-phosphate. 

Step 3 of Figure 29.7 Phosphorylation Fructose 6-phosphate is converted in step 3 to fructose 1,6-bisphosphate (FBP) by a phosphofmctokinase-catalyzed reaction with ATP (recall that the prefix bis- means two). The mechanism is similar to that in step 1, with Mg2+ ion again required as cofactor. Interestingly, the product of step 2 is the tv anomer of fructose 6-phosphate, but it is the (3 anomer that is phos-phorylated in step 3, implying that the two anomers equilibrate rapidly through the open-chain form. The result of step 3 is a molecule ready to be split into the two three-carbon intermediates that will ultimately become two molecules of pyruvate. 

Thus, in the course of reactions catalyzed by the intrinsic enzymes of the pentose phosphate cycle, two fructose 6-phosphate molecules, one glyceraldehyde 3-phosphate molecule, and three carbon dioxide molecules are produced from three glucose 6-phosphate molecules. In addition, six NADP -H2 molecules are formed. The overall scheme for the pentose phosphate cycle is ... 

This equation tells us that the conversion of one molecule of D-glucose, which contains six carbon atoms, to two molecules of lactate, which contain three carbon atoms each, is accompanied by the generation of two molecules of ATP from its constituents ADP and Pi. Note that the structure of ADP is identical to that of ATP with the exception that the terminal phosphate group is missing. 

According to a literature survey conducted by Shahalam [28], the contents of various chemicals found in the natural mined phosphate rocks vary widely, depending on location, as shown in Table 1. For instance, the mineralogical and chemical analyses of low-grade hard phosphate from the different mined beds of phosphate rock in the Rusaifa area of Jordan indicate that the phosphates are of three main types carbonate, siliceous, and silicate-carbonate. Phosphate deposits in this area exist in four distinct layers, of which the two deepest - first and second (the thickness of bed is about 3 and 3.5 m, respectively, and depth varies from about 20 to 30 m) - appear to be suitable for a currently cost-effective mining operation. A summary of the data from chemical analyses of the ores is shown in Table 2 [28]. 

This enzyme [EC 5.3.1.1], also known as triosephosphate mutase (TIM) and phosphotriose isomerase, catalyzes the interconversion of D-glyceraldehyde 3-phosphate and dihydroxyacetone phosphate (fUPAC glycerone phosphate). As pointed out by Rose, this enzyme is chiefly responsible for the largely symmetrical conversion of the two three-carbon segments of glucose to lactate and for the nearly uniform distribution of from pyruvate in the glucosyl units of hver glycogen. The... 

Interconversion between these three-carbon intermediates is a reversible reaction catalyzed by triose phosphate isomerase. 

One of the most important buffer systems in the human body is that which keeps the pH of blood around 7.4. If the pH of blood fall below 6.8 or above 7.8, critical problems and even death can occur. There are three primary buffer systems at work in controlling the pH of blood carbonate, phosphate, and proteins. The primary buffer system in the blood involves carbonic acid, H COj and its conjugate base bicarbonate, HCO3. Carbonic acid is a weak acid that dissociates according to the following reaction ... 

Another three-carbon compound, 1,3-bisphospho-glycerate (Fig. 13—4), contains an anhydride bond between the carboxyl group at C-l and phosphoric acid. Hydrolysis of this acyl phosphate is accompanied by a large, negative, standard free-energy change (AG ° =... 

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