Dehydrogenases glycerol-3-phosphate dehydrogenase

FAD Sucdnate —> furmarate3 Fatty acyl CoA —> enoyl CoAb Glycerol-3-phosphate —> dihydroxyacetone phosphate (mitochondrial)c Succinate dehydrogenase Fatty acyl CoA dehydrogenase Glycerol-3-phosphate dehydrogenase... 

The second electron shuttle system, called the malate-aspartate shuttle, is shown in Figure 21.34. Oxaloacetate is reduced in the cytosol, acquiring the electrons of NADH (which is oxidized to NAD ). Malate is transported across the inner membrane, where it is reoxidized by malate dehydrogenase, converting NAD to NADH in the matrix. This mitochondrial NADH readily enters the electron transport chain. The oxaloacetate produced in this reaction cannot cross the inner membrane and must be transaminated to form aspartate, which can be transported across the membrane to the cytosolic side. Transamination in the cytosol recycles aspartate back to oxaloacetate. In contrast to the glycerol phosphate shuttle, the malate-aspartate cycle is reversible, and it operates as shown in Figure 21.34 only if the NADH/NAD ratio in the cytosol is higher than the ratio in the matrix. Because this shuttle produces NADH in the matrix, the full 2.5 ATPs per NADH are recovered. 

GLYCEROL PHOSPHATE DEHYDROGENASE IS AN NADH OXIDIZING ENZYME RELATED TO GLYCOLYSIS 541... 

Glycerol phosphate dehydrogenase (GPDH) is indirectly associated with glycolysis and reduces dihydroxyacetone phosphate to glycerol-3-phosphate, oxidizing NADH... 

DBM dopamine P-monooxygenase GDPH glycerol phosphate dehydrogenase... 

Liver cells contain two different but closely related enzymes glycerol phosphate dehydrogenase which is specific for NAD, and acylglycerol phosphate dehydrogenase, which is NADP specific. Both enzymes have B stereospecificity for the pyridine nucleotide 93. They apparently have different metabolic functions. 

Many enzymes in the mitochondria, including those of the citric acid cycle and pyruvate dehydrogenase, produce NADH, aU of which can be oxidized in the electron transport chain and in the process, capture energy for ATP synthesis by oxidative phosphorylation. If NADH is produced in the cytoplasm, either the malate shuttle or the a-glycerol phosphate shuttle can transfer the electrons into the mitochondria for delivery to the ETC. Once NADH has been oxidized, the NAD can again be used by enzymes that require it. 

FADH is produced by succinate dehydrogenase in the citric acid cycle and by the a-glycerol phosphate shuttle. Both enzymes are located in the inner membrane and can reoxidize FADHj directly by transferring electrons into the ETC. Once FADH2 has been oxidized, the FAD can be made available once again for use by the enzyme. 

All these components are in the inner membrane of the mitochondria as shown in Figure I-I3-3. Succinate dehydrogenase and the a-glycerol phosphate shuttle enzymes reoxidize their FADHj and pass electrons directly to CoQ. 

Figure 9.18 The glycerol phosphate shuttle. In the cytosol, NADH is oxidised in a reaction in which dihydroxyacetone phosphate is reduced to glycerol 3-phosphate, catalysed by glycerol-3-phosphate dehydrogenase (NAD linked) ...

As depicted in Figure 6.8 the stability screening was based on DERA activity assay, the retro-aldol reaction of 2-deoxy-D-ribose 5-phosphate to acetaldehyde and D-glyceraldehyde 3-phosphate. D-glyceraldehyde 3-phosphate is further converted by the auxiliary enzymes triose phosphate isomerase and glycerol phosphate dehydrogenase. As the latter reaction consumes NADH it can be measured spectro-pho to metrically by the decrease in absorbance at 340 nm. 

The lipid-soluble ubiquinone (Q) is present in both bacterial and mitochondrial membranes in relatively large amounts compared to other electron carriers (Table 18-2). It seems to be located at a point of convergence of the NADH, succinate, glycerol phosphate, and choline branches of the electron transport chain. Ubiquinone plays a role somewhat like that of NADH, which carries electrons between dehydrogenases in the cytoplasm and from soluble dehydrogenases in the aqueous mitochondrial matrix to flavoproteins embedded in the membrane. Ubiquinone transfers electrons plus protons between proteins within the... 

The regulatory role of calcium ions in intermediary metabolism is well documented. Calcium has been shown to be involved in activation or inhibition of specific enzyme systems [105], For example, it activates cyclic nucleotide phosphodiesterase, phosphofructokinase, fructose 1 6 biphosphatase, glycerol phosphate dehydrogenase, pyruvate dehydrogenase phosphatase and pyruvate dehydrogenase kinase. Calcium ions inhibit pyruvate kinase, pyruvate carboxylase, Na+/K+-AT-Pase and adenylate cyclase. 

Adler, A.J., Klucznik, K.M. (1982). Glycerol phosphate dehydrogenase in developing chick retina and brain. J. Neurochem. 38 909-15. 

Link, W.A., Kausehnann, G., Mellstrdm, B., Kubl, D., Naranjo J.R. (2000). Induction of glycerol phosphate dehydrogenase gene expression during seizure and analgesia. J. Neurochem. 75 1419-28. 

Glycerol concentration can be determined with glycerol dehydrogenase (Ref. 60, Equation 19) or with glycerokinase coupled with glycerol phosphate dehydrogenase in the presence of NAD (Ref. 61, Equations 20, 21). 

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